Henry Lerner, M.D.
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to Shoulder Dystocia
of Shoulder Dystocia
- What is
- Pelvic Anatomy Related to Shoulder Dystocia
- Incidence of Shoulder Dystocia
- Recurrent Shoulder Dystocia
Injuries Following Shoulder Dystocia
Shoulder Dystocia be
Can Shoulder Dystocia and
Brachial Plexus Injury Be Prevented?
Can Shoulder Dystocia Be
Resolved Without Fetal Injury When It Does Occur?
Is All Brachial Plexus Injury
Caused by Shoulder Dystocia?
- Shoulder Dystocia
The greatest nightmare an obstetrician is
likely to face is shoulder dystocia. At an otherwise normal
delivery, just after the baby's head has emerged, the neck
suddenly retracts back against the mother's perineum causing
the baby's cheeks to puff out. The experienced obstetrician
knows at this point that the baby's anterior shoulder is
caught on the mother's pubic bone and if he or she is unable
to free up the shoulder within a few minutes the baby will
suffer irreversible brain damage or death.
Shoulder dystocia occurs in
approximately one half of one percent of all deliveries. Given
that there are 4 million babies born each year in the United
States, this delivery complication will be experienced by
roughly 20,000 women a year. The larger the baby, the more
likely it is to occur. However, even with very large babies
shoulder dystocia occurs only occasionally and sporadically.
Therefore a physician never knows when it will be encountered.
The most common serious complication
following a shoulder dystocia delivery is brachial plexus
injury. This is when the nerves in a baby's neck--the brachial
plexus--are temporarily or permanently damaged. The nerves of
the brachial plexus control the function of the arm and hand.
Injury to the upper part of the brachial plexus is called Erb
palsy while injury to the lower nerves of the plexus is called
Klumpke palsy. Both can cause significant, lifelong
Because of the gravity and
unexpectedness of shoulder dystocia it has long been a major
area of obstetrical concern. Yet despite the hundreds of
published studies about shoulder dystocia there still are
multiple, important unanswered questions:
Is shoulder dystocia predictable?
Can it be prevented?
Is there anything that can be done
when it does occur to prevent brachial plexus nerve damage?
If there is an injury, was it caused
by mismanagement on the part of the physician while
attempting to resolve the shoulder dystocia or was it an
inevitable consequence of the shoulder dystocia?
The interest obstetricians have in
these questions has been heightened in the last two decades by
the increasing influence of medical-legal issues on the
practice of medicine. As regards shoulder dystocia, it is
frequently the case that when a brachial plexus injury occurs,
an obstetrician will be charged with negligence. Such claims
are now so frequent that law suits related to shoulder
dystocia deliveries result in the second largest category of
indemnity payments in obstetrics, exceeded only by birth
In their defense, physicians contend
that shoulder dystocia is a totally unpredictable event and
that even with perfect management brachial plexus injuries
Where does the truth lie?
This web site represents an attempt to
answer this and other questions about shoulder dystocia. By
having thoroughly reviewed the published literature on
shoulder dystocia and brachial plexus injury from 1965 to the
present, it has been possible to frame comprehensive and
consistent answers to the major questions that bedevil this
area of obstetrics. It is the hope of the author that the
information presented here about the cause, preventability,
and culpability for shoulder dystocia and brachial plexus
injuries will (1) aid in improving the care given to women and
their babies and (2) will help adjudicate responsibility in
medical liability cases in which a baby has been injured
during a shoulder dystocia delivery. History
The phenomenon of shoulder dystocia has
long been recognized. Smellie, one of the earliest physicians
specializing in obstetrics, described a situation he
encountered in 1730 as follows:
Called to a gentlewoman in labor. The
child's head delivered for a long time -- but even with horrid
pulling from the midwife, the remarkably large shoulder
prevented delivery. I have been called by midwives to many
cases of this kind, in which the child was frequently lost.
Morris in 1955 gave what is now a
classic description of shoulder dystocia:
The delivery of the head with or
without forceps may have been quite easy, but more commonly
there has been a little difficulty in completing the
extension of the head. The hairy scalp slides out with
reluctance. When the forehead has appeared it is necessary
to press back the perineum to deliver the face. Fat cheeks
eventually emerge. A double chin has to be hooked over the
posterior vulvar commisure, to which it remains tightly
opposed . . .
Time passes. The child's face
becomes suffused. It endeavors unsuccessfully to breathe.
Abdominal efforts by the mother and by her attendants
produce no advance. Gentle head traction is equally
unavailing. Usually equanimity forsakes the attendants --
they push, they pull. Alarm increases. Eventually, "by
greater strength of muscle or by some infernal juggle," the
difficulty appears to be overcome, and the shoulder and
trunk of a goodly child are delivered. The pallor of its
body contrasts with the plum-colored cyanosis of the face,
and the small quantity of freshly expelled meconium about
the buttocks. It dawns upon the attendants that their
anxiety was not ill founded, the baby lies limp and
voiceless, and only too often remains so despite all efforts
Perhaps the most famous case of
shoulder dystocia was that involving Prince William of Germany
who subsequently became Kaiser Wilhelm II in 1888. It seems
that William was in breech position at birth and was
manipulated by several physicians and a midwife during
delivery. Apparently the baby was not breathing when it
emerged, but by "continuous rubbing . . . dousing in a hot
bath, and a series of short, sharp slaps on his buttocks" the
doctors managed to get the child to breathe. The third day
after delivery the midwife noticed that William's left arm was
slack. It was thought that the arm had been "wrenched out of
the socket" and some of the muscle tissue torn. In addition it
is suspected that there were several moments of asphyxia which
might have caused slight brain damage. It has been postulated
that this was the cause of William's later hyperactivity and
emotional instability. He may also have suffered slight
cerebral palsy. For the rest of his life, William's "withered"
left arm was concealed from the public by careful posing for
Shoulder dystocia occurs when, after
delivery of the fetal head, the baby's anterior shoulder gets
stuck behind the mother's pubic bone. If this happens, the
remainder of the baby does not follow the head easily out of
the vagina as it usually does during vaginal deliveries.
This simple definition of shoulder
dystocia, however, glosses over many complexities. For
example, should a delivery be categorized as involving
shoulder dystocia only when there is some time delay -- 60
seconds is often suggested in this context-between the
delivery of a baby's head and shoulders? Or is shoulder
dystocia present any time that a delivering physician finds
that the shoulders cannot be delivered with the normal amount
of downward traction on the fetal head? Some have suggested
that the definition of true shoulder dystocia requires that an
obstetrician had to perform special maneuvers in order to
deliver the shoulders.
Exactly how shoulder dystocia is
defined is more than just a semantic issue. It sets the
parameters for the collection of statistics related to
shoulder dystocia, a necessity for research aimed at
decreasing shoulder dystocia related injuries. It also
determines when a baby's injuries might be attributed to a
physician's actions during labor and delivery.
image to view larger imagePelvic
anatomy related to shoulder dystocia
It is necessary to know something about
the anatomy of the fetus and the maternal pelvis in order to
understand how shoulder dystocia comes about and how it causes
the injuries it does.
As the accompanying diagram shows, the
maternal pelvis is composed of a series of bones forming a
circle protecting the pelvic organs. The front-most bone is
the symphysis pubis. It is on this structure that a baby's
anterior shoulder gets caught during a delivery complicated by
shoulder dystocia. The bone at the back of the maternal pelvis
is the sacrum. Because of its shape, it generally serves as a
slide over which a baby's posterior shoulder can descend
freely during labor and delivery. The side walls of the
maternal pelvis, although very important in determining the
ease of the process of labor in general, usually do not
contribute to shoulder dystocia.
image to view larger image
In normal vaginal deliveries the head
of the baby, called the "vertex", emerges first. During labor,
the soft, mobile bones of the fetal head can "mold"-alter
their shape -- and, to a slight degree, overlap. This
facilitates the fetal head fitting into and through the
maternal pelvis. The baby's shoulders, likewise being
flexible, usually follow the delivery of the baby's head
quickly and easily. But for this to happen, the axis of the
fetal shoulders must descend into the maternal pelvis at an
angle oblique to the pelvis's anterior-posterior
dimension. This position affords the shoulders the most room
for their passage. If instead the shoulders line up in a
straight front-to-back orientation as they are about to emerge
from the mother's pelvis, there will often be insufficient
room for them to squeeze through. The back of the mother's
pubic bone then forms a shelf on which the baby's anterior
shoulder can get caught. If this happens, the shoulders cannot
deliver and a shoulder dystocia results.
Shoulder dystocia can also occur if
the posterior shoulder of a baby gets caught on its mother's
sacrum. This is a far less common cause of shoulder dystocia.
The sacrum, having no protrusions equivalent to that of the
pubic bone, is far less likely to impede the descent of the
baby's posterior shoulder.
As can be readily appreciated, it is
the relative sizes of the fetal head, shoulders, and chest
compared to the shape and size of the maternal pelvis that
determine how smoothly a delivery will go. Usually it is the
fetal head that has the largest dimensions. Thus if it can
pass through the maternal pelvis without difficulty, the rest
of the baby usually follows easily. However, when the
dimensions of the fetal shoulders or chest rival those of its
head, the chances of a shoulder dystocia occurring are much
increased. Such situations occur more frequently both in large
babies and in babies of diabetic mothers.
In large babies, much of the excess
growth that occurs is in the chest and abdominal areas. In
these babies the dimensions of the shoulders and chest tend to
be disproportionately larger than those of the head. This
trend is exaggerated in babies of diabetic mothers. Multiple
studies have shown that babies of diabetic mothers more
frequently have larger ratios of shoulder circumference to
head circumference than do their peers born of nondiabetic
mothers. Babies of diabetic mothers also have greater arm
circumference, larger triceps folds, and a higher percentage
of body fat. Since larger babies are more likely to "get
stuck", much of the work in the field of shoulder dystocia has
been targeted at attempting to predict which babies will be
larger than normal, especially when their mothers are
Except in extraordinary circumstances,
once the fetal head and shoulders have been delivered the
remainder of the fetal trunk and legs slide out easily. Such
extraordinary circumstances preventing easy delivery of the
fetal body might be when:
- A fetus has a large abdominal or
lower back tumor,
- The umbilical cord is wrapped
tightly around the baby's neck, or
- There is a severe constriction of
the uterine muscle -- "contraction rings" -- trapping the
baby in the uterus.
The above applies only to vertex or
headfirst deliveries. Breech deliveries, where the fetal legs
and buttocks emerge first from the vagina, can also result in
injury to the fetal arms and neck, producing the brachial
plexus injuries discussed above. However, since these and
other sorts of injuries to babies from vaginal breech
deliveries occur at a relatively high rate, most breech babies
in the United States are now delivered by cesarean section.Incidence
The incidence of shoulder dystocia is
generally reported to be between 0.5 % and 1.5% with scattered
reports listing values both higher and lower. Those studies
involving the largest number of deliveries have usually found
the rate of shoulder dystocia in a general population to be
0.5% - 0.6%. The "true" incidence of shoulder dystocia,
however, is very much dependent upon how it is defined, how it
is reported, and the characteristics of the population being
The accuracy of reporting is an
important variable in shoulder dystocia statistics. Many
obstetricians are reluctant to write down in their delivery
notes that a shoulder dystocia has occurred for fear that this
will be a red flag attracting a malpractice suit should it
later turn out that the baby has suffered an injury. Some
studies have shown that only 25% to 50% of shoulder dystocias
-- as noted by objective observers in a delivery room -- are
recorded by the delivering physician.
How one defines shoulder dystocia, of
course, affects its reported incidence. Some obstetricians
will only report a delivery as involving shoulder dystocia if
they had to employ specific maneuvers to deliver the baby's
anterior shoulder. Others will record shoulder dystocia if
there is any delay in the emergence of the shoulder following
delivery of the head. In some cases a physician will only
record "shoulder dystocia" when a fetal injury has occurred.
Finally, the characteristics of the
delivery group being measured will affect statistics on
shoulder dystocia. A study evaluating the incidence of
shoulder dystocia utilizing only large babies or only infants
of diabetic mothers as subjects will have a much higher
reported incidence of shoulder dystocia than if the population
were a general one containing both small and large babies and
the normal percentage of mothers having diabetes.
Several of the more recent studies
have shown a slightly higher incidence of shoulder dystocia
than has been recorded in the past, reaching just above 1% of
all deliveries. The question has therefore been asked, "Is the
rate of shoulder dystocia increasing?" While there is as yet
no definitive answer to this question, several hypotheses have
been given to explain this possible trend:
1. On average babies are
significantly larger then in years past. The percentage of
very large baby's (>4000gms) in one study has gone up 300%
between 1970 and 1988.
2. Over the last several decades
there has been a marked increase in average maternal weight,
average maternal weight gain during pregnancy, and the
number of diabetic women having babies. All of these factors
could be expected to increase the incidence of shoulder
3. The increased focus of attention
among obstetricians about shoulder dystocia deliveries may
have heightened awareness about it and increased reporting
The question as to whether or not women
who have had a shoulder dystocia in a previous delivery are
more likely to have one again in a subsequent delivery is an
extremely important one. This information will help guide how
future deliveries in these women are managed.
It appears from the literature that
the risk of recurrent shoulder dystocia is substantial: 10 to
15%. Moreover, women who have had a shoulder dystocia delivery
that resulted in injury to the fetus have an even greater risk
of having a recurrent shoulder dystocia and subsequent fetal
injuries following shoulder dystocia
Following shoulder dystocia deliveries,
20% of babies will suffer some sort of injury, either
temporary or permanent. The most common of these injuries are
damage to the brachial plexus nerves, fractured clavicles,
fractured humeri, contusions and lacerations, and birth
Brachial plexus injury
The brachial plexus consists of the
nerve roots of spinal cord segments C5, C6, C7, C8, and T1.
(See accompanying diagram). These nerve roots form three
trunks which divide into anterior and posterior divisions. The
upper trunk is made up of nerves from C5 and C6, the middle
trunk from undivided fibers of C7, and the lowermost trunk is
made up of nerves from C8 and T1.
image to view larger image
There are two major types of brachial
plexus injury: Erb palsy and Klumpke palsy.
Erb palsy, the more commonly occurring
of the two forms of brachial plexus injury, involves the upper
trunk of the brachial plexus (nerve roots C5 through C7). This
palsy affects the muscles of the upper arm and causes abnormal
positioning of the scapula called "winging". The supinator and
extensor muscles of the wrist that are controlled by C6 may
also be affected. Sensory deficits are usually limited to the
distribution of the musculo-cutaneous nerve. Together, these
injuries result in a child having a humerus that is pulled in
towards the body (adducted) and internally rotated. The
forearm extended. Some have described this as the "waiters
Klumpke palsy involves lower trunk
lesions from nerve roots C7, C8, and T1. In this injury the
elbow becomes flexed and the forearm supinated (opened up,
palm-upwards) with a characteristic clawlike deformity of the
hand. Sensation in the palm of the hand is diminished.
image to view larger image
It has been traditionally thought that
most brachial plexus injuries result from stretching of the
nerves of the brachial plexus during delivery. While this
likely accounts for many brachial plexus injuries, reports of
such injuries following deliveries in which there was no
shoulder dystocia has led investigators to question whether or
not brachial plexus injuries might have other etiologies. Such
etiologies might be intrauterine cerebrovascular accidents
(strokes), overstretching of the brachial plexus from fetal
movement during the pregnancy, or basic maldevelopment of the
In some brachial plexus injuries
sympathetic nerve fibers that traverse T1 can be damaged. This
can result in depression of the eyelid and drooping of the
mouth on the affected side, a constellation of symptoms called
image to view larger image
Incidence of brachial plexus injury
Brachial plexus injury is the classic
injury following shoulder dystocia. First described by
Duchenne in 1872, it occurs following roughly 10% of all
shoulder dystocia deliveries as reported in a variety of
Gherman (1998) 16.8%
McFarland (1996) 8.5%
Bofill (1997) 9.5%
Baskett (1995) 13%
Stallings (2001) 12.7%
Nocon (1993) 15.1%
The incidence of shoulder dystocia
rises with many factors, the most prominent of which are the
size of the baby and maternal diabetes status. Given that
roughly one half of 1% of all babies experience shoulder
dystocia during delivery and that approximately 10% of
shoulder dystocia deliveries result in brachial plexus
injuries, the theoretical rate of brachial plexus injury
following shoulder dystocia is roughly one in 2000 deliveries.
This prediction is confirmed by observation.
Brachial plexus injuries can also
occur without there having been a shoulder dystocia. There are
multiple reports in the literature of brachial plexus injuries
following vaginal deliveries without shoulder dystocia,
subsequent to breech deliveries, and even after otherwise
uncomplicated cesarean sections. In fact, the rate of brachial
plexus injury in which no shoulder dystocia was reported has
been quoted to be as high as 40% to 50%. These findings are
discussed in detail on subsequent pages on this site.
The natural history of brachial
Fortunately, most brachial plexus
birth injuries are transient. The majority of such injuries
resolve by three months, with a range of two weeks to 12
months. Only 4 to 15% result in some degree of permanent
Rate of brachial plexus injuries
that persist permanently
Eckert (1997) 5-22%
Johnson (1979) 7.8%
Graham (1997) 20%
Sandmire (1988) 11.8%
Nocon (1995) 4%
Patients with upper lesions -- Erb
palsy -- have a better prognosis than those with lower
brachial plexus injuries-Klumpke palsy. Whereas upwards of 90
to 95% of all Erb palsies totally resolve, only 60% of Klumpke
palsies do. Interestingly, those brachial plexus injuries
associated with non-shoulder dystocia deliveries persist more
often than those occurring following deliveries in which a
shoulder dystocia was documented.
Brachial plexus injuries can also
produce secondary effects. Muscle imbalances produced in the
hand, arm, and shoulder may result in osseous deformities of
the shoulder and elbow and in dislocations of the radial head.
The development of the affected arm may be compromised,
resulting in its being as much as 10 cm shorter than the
Treatment options and prognosis
As mentioned, the majority of brachial
plexus injuries will resolve spontaneously over the course of
several months to a year. Physical therapy is usually employed
within weeks of birth to help strengthen muscles whose nerve
supply has been damaged. For those injuries that are permanent
there are two modes of therapy.
First, physical therapy can strengthen
muscles that are only partially denervated, strengthen
surrounding muscles to compensate for functional loss, and
improve the range of motion of the affected shoulder, arm,
elbow, or hand.
Second, surgical therapy in the form
of nerve grafting or muscle transposition may be undertaken.
There is, however, great controversy about the efficacy of
such surgical procedures in improving the outcome of those
with brachial plexus injuries. Several orthopedic and
neurosurgeons from around the country who do this sort of
surgery frequently report various degrees of improvement in
many of their patients. Others in the field, however, refute
these claims and feel that there is little or no benefit to
Other physical injuries following
shoulder dystocia deliveries
The second most common injury suffered
by infants following shoulder dystocia deliveries is a
fractured clavicle. The incidence of this injury following
shoulder dystocia is 10%.
If the fetal shoulders and chest are
relatively large in relation to the maternal pelvis,
significant pressure may be placed on them as they pass
through the birth canal following delivery of the fetal head.
In some infants, this pressure causes the clavicle to
fracture. The overlapping of the ends of the broken clavicle
reduces the diameter of the fetal chest and intra-shoulder
distance and allows them to be delivered. This "safety valve"
effect may in fact help reduce the incidence of severe
brachial plexus injury.
The baseline clavicular fracture rate
for all deliveries appears to be about 0.3%. Despite the fact
that shoulder dystocia increases the risk of clavicular
fracture 30 fold, approximately 75% of clavicular fractures
are not associated with shoulder dystocia. Interestingly,
although there are multiple reports of brachial plexus
injuries following cesarean sections, clavicular fractures
following cesarean sections are extremely rare.
This occurs in approximately 4% of
infants with shoulder dystocia deliveries. Such injuries heal
rapidly and are rarely result in litigation.
The force with which the infant's
shoulder is compressed against the maternal pubic bone and the
pressure of the deliverer's hands on the fetus while
performing various maneuvers to effect delivery will often
result in bruises on the baby's body. Such bruising has often
been cited by plaintiff attorneys as evidence that a baby has
been handled roughly at delivery despite the fact that such
bruises are common even in routine deliveries not involving
shoulder dystocia or fetal injury.
The most feared complication of
shoulder dystocia is fetal asphyxia. It has been frequently
demonstrated in both animal experiments and in retrospective
analyses of babies born following dramatic cessation of
umbilical blood flow (placental abruption, uterine rupture,
etc.) that if babies are not delivered within five to 10
minutes they will suffer irreversible neurologic damage or
death. Wood, in an often-quoted article from 1973, showed that
in the time between delivery of the head and trunk of an
infant, the umbilical artery pH declines at a rate of 0.04
units per minute. This means that at the five-minute mark
following delivery of the fetal head, the baby's pH may have
dropped from 7.2 -- a common level after several hours of
pushing -- to 7.0, the level that defines asphyxia. By 10
minutes the pH would have dropped to 6.8. Ouzounian (1998)
reported that of 39 babies whose deliveries involved shoulder
dystocia, 15 who suffered brain injury averaged a
head-to-shoulder delivery interval of 10.6 minutes while the
24 babies also born following shoulder dystocia but without
brain injury had a head-to-shoulder delivery interval of only
4.3 minutes. Cerebral palsy and fetal death are rare but
unfortunately not unheard of consequences of prolonged
head-to-shoulder delivery intervals following shoulder
The reason for the increasing acidosis
and asphyxia that occurs during a shoulder dystocia delivery
is that once the fetal head emerges from the mother, the
baby's umbilical cord becomes tightly compressed between its
body and that of the mother's birth canal. This significantly
decreases or totally cuts off blood flow between the mother
and infant. If the pressure on the cord is not rapidly
relieved, the consequences of cessation of lack of umbilical
flow -- decreased delivery of oxygen to the fetus -- will
The mother, too, is at some risk when
shoulder dystocia occurs. The most common complications she
may suffer are excessive blood loss and vaginal and vulvar
Significant blood loss, which occurs
in one quarter of all shoulder dystocia deliveries, may be
seen either during the delivery or in the postpartum period.
Its usual causes are uterine atony or lacerations of the
maternal birth canal and surrounding structures. Such
lacerations may involve the vaginal wall, cervix, extensions
of episiotomies, or tears into the rectum. Uterine rupture has
also been reported.
Because of the pressure directed
upwards towards the bladder by the anterior shoulder in
shoulder dystocia deliveries, post-partum bladder atony is
frequently seen. Fortunately, it is almost always temporary.
Occasionally the mother's symphyseal joint may become
separated or the lateral femoral cutaneous nerve damaged, most
likely the result of overaggressive hyperflexion of the
maternal legs during attempts at resolving the shoulder
Even though shoulder dystocia occurs
in only 0.5% to 1.0% of all deliveries, the fact that there
are approximately 4 million deliveries a year in United States
means that many thousands of mothers and babies will
experience this obstetrical complication. A little math tells
--If the rate of occurrence of
shoulder dystocia is approximately 0.5%, and
--If the rate of brachial plexus
injury is 10% in these deliveries, and
--If the rate of permanent injury is
10% of all brachial plexus injuries,
then the rate of permanent brachial
plexus injury will be one in 10,000 to one in 20,000
This means that there will be
approximately 200 to 400 babies born each year in the United
States with permanent brachial plexus injuries following
shoulder dystocia deliveries. In addition, there will be
babies who will suffer severe central neurologic injury such
as cerebral palsy from asphyxia. There will even be babies who
will die following severe shoulder dystocias. It is for these
reasons that shoulder dystocia injuries have become an
important area of medical -- and medical-legal -- concern.
The medical concern involves trying to
find ways of preventing shoulder dystocia related injuries.
The best way to do this, of course, would be to prevent
shoulder dystocia from occurring. If this is not possible,
then it is necessary to try to find ways to resolve shoulder
dystocias with minimal fetal injury when they do occur.
However, since many brachial plexus injuries are seen
following deliveries where there was no shoulder dystocia,
even perfect prediction and prevention of shoulder dystocias
would not entirely eliminate the occurrence of brachial plexus
The medical-legal implications of the
above are obvious: Given a severely injured infant, if it can
be shown that a physician was negligent either in allowing a
shoulder dystocia to occur or in his or her handling of the
shoulder dystocia once it did occur, then according to our
legal system, that physician will be held liable for damages
to the injured baby and his or her family.
dystocia be anticipated accurately?
Up until 2006, the answer to this question by the vast majority of experts in obstetrics would have been a resounding “No!” In fact, the majority of the obstetrical literature still indicates that this is the case. However new work by several investigators (Gudmundsson 2005, Mazouni 2006) has confirmed a linkage between maternal size, fetal weight, and shoulder dystocia. Moreover, based on this principle, Dr. Emily Hamilton in Montréal appears to have developed a means by which the majority of those pregnant women destined to have a shoulder dystocia can be detected (Dyachenko, Hamilton 2006).
It must be emphasized that this predictive tool -- called the CALM Shoulder ScreenTM (patent pending) -- is currently undergoing its first clinical applications. It has not been available to obstetricians in the past, and is by no means the current standard of care. However, if the results thus far demonstrated by this predictive technique continue to be validated, the standard of care for the preventative management of shoulder dystocia may soon change.
First, however, let’s review the data that obstetricians have had up until now in attempting to predict which mothers and babies would experience shoulder dystocia.
In the past, there have been physicians who have claimed that shoulder dystocia could be predicted. Hassan (1988) stated,
"In the majority of cases shoulder
dystocia can be anticipated. Risk factors include maternal
obesity, diabetes, preeclampsia, prolonged gestation, and
fetal macrosomia. A male infant is at a greater risk for
macrosomia and dystocia."
O'Leary, in his 1992 book, Shoulder
Dystocia and Birth Injuries, concurred.
However, this has been an overwhelmingly a minority opinion. The vast majority of obstetricians, including those who have done the most work on shoulder dystocia and brachial plexus injuries, up till now have concluded that it is impossible with any degree of certainty to predict in which deliveries shoulder dystocia will occur. The key issue involved is "certainty". As will be shown, there are multiple "risk" factors for shoulder dystocia. Mothers and babies having these risk factors are, in an absolute sense, more likely than mothers and babies without these factors to experience shoulder dystocia. But whether the predictive value of such factors as currently measured is high enough to be useful clinically, that is, to justify changes in labor management plans in hopes of avoiding shoulder dystocia, is what is at issue. Moreover, as with most statistical questions in medicine, the predictability of shoulder dystocia has to be looked at from two directions:
Sensitivity: Are the risk
factors associated with shoulder dystocia able to accurately
identify most babies who will have shoulder dystocia at
Positive predictive value:
What percentage of mothers and babies having these risk
factors will, in fact, experience shoulder dystocia?
In the case of shoulder dystocia, its infrequent rate of occurrence (0.5%) and the low positive predictive value of risk factors for it have severely impeded the ability of obstetricians to utilize such information to advantageously alter clinical care.
The past medical literature has confirmed this overwhelmingly. Gherman (2002), among current leaders in the study of shoulder dystocia, has said the following:
Most of these preconceptions and
prenatal risk factors have extremely poor positive
predictive values and therefore do not allow the
obstetrician to accurately and reliably predict the
occurrence of shoulder dystocia.
Resnick (1988), discussing the ability of obstetricians to predict when shoulder dystocias will occur, stated that "the diagnosis [of shoulder dystocia] will often be made only after delivery of the fetal head."
Lewis (1998) noted that only 25% of shoulder dystocia cases had at least one significant risk factor.
Geary (1995) reported that when all antenatal risk factors for shoulder dystocia were taken into account, the positive predictive value was less than 2% for individual factors and less than 3% when multiple factors were combined.
The bottom line is this: In the past, nowhere in the literature were there studies that showed that the sensitivity or positive predictive value for predicting shoulder dystocia was high enough to justify obstetrical interventions in hopes of avoiding it.
Categories of risk factors
The risk factors for shoulder dystocia
can generally be divided into three categories:
Preconceptual -- before
Antepartum -- during
Intrapartum -- during labor
Preconceptual risk factors for
1. Previous shoulder dystocia
Previous shoulder dystocia proves to
be one of the most accurate predictors for recurrent shoulder
dystocia. This makes perfect sense. The pelvic anatomy of a
woman does not change in between pregnancies. Moreover, second
and subsequent babies are likely to be larger than first or
The risk of a woman having a repeat
shoulder dystocia once having had one, as reported from
various authors, is:
Smith (1994) 12%
Ginsburg (2001) 11%.
Gherman (2002) 11.9%
This compares with the baseline risk
for shoulder dystocia of 0.5%. Because of this significant
increase in risk -- approximately 20-fold -- some obstetricians
have proposed "once a shoulder dystocia, always a cesarean".
2. Maternal obesity
A mother's weight, likewise, proves to
be significantly correlated with shoulder dystocia. Emerson
showed (1962) that in his series shoulder dystocia occurred
twice as often in obese women as it did in normal weight
women: 1.78% versus 0.81%. Sandmire (1988) estimated that the
relative risk of shoulder dystocia in women with a
prepregnancy weight of greater than 82 kg (181 lbs) was 2.3.
However whether this is a primary
effect or merely reflects the fact that obese women tend to
have large babies is not clear. To answer this question would
require a study evaluating the rates of shoulder dystocia
correlated with both maternal and fetal weight categories.
Given the fact that more pregnant women than ever are obese,
and that obesity has a marked correlation with fetal
macrosomia, it is likely that the rate of shoulder dystocia
will be seen to increase over the next decade.
But there are major problems with attempting to use obesity by itself as a predictor of shoulder dystocia. Although obese women do have an incidence of shoulder dystocia several fold higher than that of thinner women, even the most pessimistic reports -- such as that by Hernandez in 1990 -- show a rate of shoulder dystocia in women weighing over 250 lbs. of no more than 5%. Thus even in this high risk population, 95% of extremely obese women will not have a shoulder dystocia at delivery. Thus any intervention undertaken based solely on the relationship between maternal weight and macrosomia would be without justification for 19 of 20 of such women.
3. Maternal age
Some studies have claimed maternal age
to be a risk factor for shoulder dystocia. But careful
analysis reveals that maternal age is a risk factor for
shoulder dystocia only in so far as maternal obesity,
diabetes, excessive weight gain, and instrumental deliveries
are all more common in older women. These, of course, are all
themselves risk factors for shoulder dystocia. In one of the
few studies looking at the correlation between maternal weight
and shoulder dystocia in isolation, Bahar (1996) did not find
any difference in shoulder dystocia based on maternal age
4. Abnormal pelvis
O'Leary, in his book on shoulder
dystocia, places great significance on the abnormal pelvis as
a risk factor for shoulder dystocia -- but offers no data to
support his claim. Although it would make sense that a
decrease in certain pelvic dimensions would increase the
possibility of a baby's anterior shoulder getting caught on
the maternal pubic bone, there are no reports in the
literature demonstrating a relationship between shoulder dystocia and objectively-measured pelvic shape.
Moreover, the use of pelvimetry -- x-ray
or other measurement of pelvic dimensions -- in obstetrics was
discarded years ago, for several reasons:
1. Except in the very most extreme
cases of congenital or pathological pelvic deformity, there is
poor correlation between pelvic size and a woman's capacity to
2. The ability to more accurately
monitor babies in labor enables obstetricians to safely allow
labor itself to be the test of whether or not a baby will
"fit" into and through the maternal pelvis.
In a 10-year series collected from
Boston's Beth Israel Hospital covering the years 1975 to 1985,
Acker (1988) showed that there were more Erb palsies in babies
born to multiparous women then to primigravida women. He
attributed this to a marked increase in precipitous labors in
such women. In his series he noted that 31.8% of all babies
with Erb palsy had experienced a precipitous delivery.
But as with maternal age, by the time
a woman becomes "multiparous", she is old enough to have an
increased risk of having other risk factors for shoulder
dystocia such as larger babies, obesity, and diabetes.
Moreover, only multiparous women could have the very
significant risk factor of having had a previous shoulder
dystocia. Thus most experts feel any relationship between
multiparity and shoulder dystocia is secondary to other, more
primary, risk factors.
Summary of preconceptual risk factors
- Previous shoulder dystocia significantly increases the risk of repeat shoulder dystocia
- Shoulder dystocia is seen more
commonly with increased maternal age, obesity, and multiparity
in reality these are only markers for the increased risk of
more primary risk factors
- There is no evidence linking the
"abnormal pelvis" to shoulder dystocia
B. Antepartum factors risk factors for
Macrosomia is far and away the most
significant risk factor for shoulder dystocia. It is the
factor that has been most studied and most often proposed as a
potential target for manipulation in hopes of reducing the
number of shoulder dystocia deliveries. Some authors go so far
as to claim that no other risk factor has any independent
predictive value for the occurrence of shoulder dystocia.
The most obvious confirmation of this
relationship consists of those studies measuring the
percentage of babies in different weight groups that
experienced shoulder dystocia. What is vitally important to
keep in mind when considering such data, however, is that
these are the weights ascertained after delivery. They were
not available to the obstetrician before delivery in making
his or her clinical decisions as to how the delivery should be
Acker (1985) found that babies
weighing over 4500gms experienced shoulder dystocia 22.6% of
the time. The shoulder dystocia rate in his general population
was 2%. His report showed the following:
weight in Nondiabetic women
Percent shoulder dystocia
Less than 4000 g
4000g - 4499 g
Greater than 4500 g
More than 70% of all shoulder
dystocias in his study occurred in infants weighing more than
Kolderup (1997), in a review of 2924
macrosomic deliveries at UCSF, reported that macrosomic
infants have a six fold increase in significant injury from
shoulder dystocia deliveries compared with controls.
Jackson (1988) showed in his series of
8258 deliveries that the average birth weight of babies who
suffered brachial plexus injuries was 4029 g., whereas the
average birth weight of all deliveries was 3160 g,
Lazer (1986) reported that the
shoulder dystocia rate for infants weighing more than 4500 g
was 18.5% while for "smaller babies" in his series the rate
Nisbet (1998) published a chart
showing similar data:
Percent shoulder dystocia
Sandmire (1998) likewise showed that
the incidence of shoulder dystocia significantly increased
with birth weight:
Rate of shoulder dystocia
What is macrosomia?
The definition of macrosomia has
varied both through the years and according to the author
writing about it. The various cutoff points used to define
macrosomia have been 4000 g, 4500 g, and 5000 g. Often a
distinction has been made between macrosomia in nondiabetic
versus diabetic mothers, the bar being set lower for the
fetuses of diabetic mothers. In general, in babies born to
nondiabetic mothers 5% to 7% will weigh more than 4000 g; 1%
will exceed 4500 g.
One of the most important factors
about macrosomia is the differential rate of growth of the
fetal head, chest, and trunk as gestation proceeds, both in
the babies of diabetic and of nondiabetic mothers. Until 36-38
weeks, the fetal head generally remains larger than the trunk.
Between 36 and 40 weeks, however, the relative growth of the
abdomen, chest, and shoulders begins to exceed that of the
fetal head. This is especially the case in babies of diabetic
mothers where glucose substrate levels are higher in both the
mother and fetus. Thus both in prolonged gestation and in
babies of diabetic mothers the size of a baby's trunk is
likely to increase, increasing its chances of shoulder
How is fetal weight predicted and
how accurate are these predictions?
Although the correlation between fetal
weight and shoulder dystocia is of great interest to
obstetricians, knowing about this relationship is of no use
unless fetal weight -- and the corresponding increased risk of
shoulder dystocia -- can be predicted prior to delivery. How
good, therefore, are our current techniques for estimating
Traditionally, fetal weight has been
estimated by measurement of uterine height and by Leopold
maneuvers. "Leopold maneuvers" is the name given to palpation
of the maternal abdominal wall a series of four specific steps
in order to determine fetal position, fetal presentation, and
an estimate of the size of the baby.
Such estimates, however, are
notoriously inaccurate. Studies have shown grave discrepancies
between estimation of fetal weight by experienced
obstetricians and actual fetal weight at delivery. Moreover
these studies show that the same obstetrician will make
different estimates of fetal weight on the same maternal
abdomen when repeatedly checked at close intervals.
With the advent of ultrasonic fetal
evaluation in the 1970's, it was hoped that a more accurate
means of assessing fetal weight was at hand. Many papers were
published presenting various formulas for ultrasound
estimation of fetal size. Most of these involved some
combination of measurements of fetal head and abdominal
dimensions and fetal femur length. However comprehensive
analyses of these various ultrasound formulas have concluded
that none are consistently more accurate than being within 10
to 15% of actual birth weights. Chauhan in 1995 went so far as
to say that in more than half of the models for ultrasound
prediction, clinical predictions by obstetricians were as or
more accurate. This was found to be especially true in larger
From these data it appears that
sonographic models are not significantly superior to clinical
examination in detecting newborns with birth weight's greater
than or equal to 4000 g.
Another study by Chauhan (1992) showed
that pregnant women themselves were more accurate than either
ultrasound or physician clinical estimates in determining the
birth weights of their infants.
There are many studies that confirm
the inability of any current diagnostic technique to determine
fetal weight prior to birth to any better than 10-15% above or
below the true weight:
Delpapa (1991): Only 48% of estimates
of fetal weight as determined by ultrasound within three days
of birth were within 500 g of the final fetal weight.
Benson (1987): The use of ultrasound
formulas to predict macrosomia was correct in only 47% of
Jazayeri (1999): Using a formula based
on ultrasound abdominal circumference in an attempt to
determine which babies would weigh over 4500gmshe obtained a
positive predictive value of only 9%.
As discussed above, post term growth
and maternal diabetes result in the fetal trunk growing larger
relative to the fetal head. The same pattern of
disproportionate growth occurs with babies that are large for
any reason, including inherent genetic predisposition. This is
why macrosomic babies have a higher incidence of shoulder
dystocia. In a normally proportioned baby, once the head is
delivered the fetal shoulders and body usually deliver easily.
With shoulders and trunk bigger than the fetal head, it is
much more likely that they will get stuck.
Several investigators have sought to
measure the differences in size between fetal shoulders,
trunks, and head circumferences to see if there existed a
certain ratio at which the risk of shoulder dystocia became
prohibitively high. Hopewood (1982) proposed that when the
transthoracic diameter is 1.5 cm larger than the biparietal
diameter, shoulder dystocia would be significantly increased.
Kitzmiller in 1987 developed a formula involving a CT scan of
fetal shoulders by which he was able to predict fetal weight
with good accuracy: a positive predictive value of 78% for
predicting birth weights over 4200 g. with a negative
predictive value of 100%.
However, several authors have refuted
the utility of using the relationship between measurements of
different anatomic structures to predict shoulder dystocia.
Benson (1986), while acknowledging that femur length/abdominal
circumference ratios differ in macrosomic vs. nonmacrosomic
fetuses, claimed that there is too much overlap between the
larger and smaller groups in any formula protocol to be
clinically useful. He states in his paper that "for no cutoff
value of these measurements is there a high sensitivity and
Thus the question: Can shoulder
dystocia be reliably predicted by estimating fetal weight?
The problems with attempting to
estimate which fetuses will be macrosomic and using this
information as a tool for predicting shoulder dystocia are
In the first place, it is the general
conclusion of most obstetrical experts who have studied this
issue that predicting macrosomia is unreliable. If macrosomia
cannot be reliably determined, it is hard to try to use it to
predict shoulder dystocia.
Secondly, only a very small percentage
of babies, even of those who have macrosomia, go on to develop
shoulder dystocia. This presents a significant obstacle to the
use of estimates of fetal weight as a tool for deciding when
to change clinical management in hopes of preventing shoulder
These difficulties are highlighted in
the data presented below:
Resnick (1980) found that shoulder
dystocia occurred in only 1.7% of 1409 infants born at Johns
Hopkins Hospital weighing more than 4000 g.
Acker (1986) pointed out that although
the relative frequency of shoulder dystocia varied directly
with increasing birth weight, almost half of the shoulder
dystocias occurred in deliveries involving average and smaller
babies. This is because there were so many more of them.
Forty-seven percent of all shoulder dystocias at the Beth
Israel hospital during the time of his study occurred in
babies weighing less than 4000 g, a weight category which
encompassed 91.2% of his total delivery population. Thus any attempt to use estimates of fetal weight as an isolated factor to reduce the incidence of shoulder dystocia would miss half of all shoulder dystocias -- even if macrosomia could be accurately measured.
Gonen (2000) evaluated 17 babies with
brachial plexus injuries from a population of 16,416
deliveries. Only three of these injured babies were macrosomic.
Geary (1995) found that the positive
predictive value of a birth weight of more than 4000 g for
predicting shoulder dystocia was only 3.3%.
Delpapa's 1991 study showed that, at
his institution, 50% of babies estimated to weigh more than
4000gm in fact had birth weights below 4000gm -- a false positive
rate for predicting macrosomia of 50%!
Levine in 1992 showed that if
macrosomia was defined as the 90th percentile of fetal weight
for a given gestational age, then sonographic prediction of
macrosomic was wrong 50% of the time both in underestimating
and overestimating fetal weight. Similar unsuccessful attempts
to accurately ascertain fetal birth weight during the
antenatal or intrapartum period have been published by:
Sacks DA (2000)
The American College of Obstetricians
and Gynecologists bulletin on shoulder dystocia states that
ultrasound has a sensitivity of only 22 to 44% and a positive
predictive value of only 30 to 44% in predicting macrosomia.
Thus up until now, as has been shown, it has been the general consensus of obstetricians who have done research in the area of shoulder dystocia that the occurrence of shoulder dystocia based on estimations of fetal weight could not be reliably predicted.
El Madany sums up this issue well in
his 1990 paper:
"Even if certain combinations of risk
factors exist which could with high likelihood isolate which
babies experienced shoulder dystocia, the inability to predict
macrosomia with the requisite degree of certainty on which
such a clinical suspicion is based precludes making active
action protocols. Until the macrosomic infant can be
accurately identified, no reasonable risk factor profile can
Sandmire, in his 1993 article,
"Any approach using ultrasound would
have to demonstrate that its use improves newborn or maternal
outcome without disproportionate increases in morbidity and
mortality. A barrier to achieving this goal is the inaccuracy
associated with ultrasonic estimations of fetal weight. The
current ultrasonic procedures for estimation of fetal weight
are not accurate enough for detecting macrosomia defined by
weight criteria. And even if clinicians could determine fetal
weight accurately, the frequency of persistent fetal injuries
associated with vaginal birth of the macrosomic fetus is so
low that induction of labor or cesarean birth is not justified
on that basis. Delivery decisions based on inaccurate
estimated fetal weight should be avoided."
Thus, while macrosomia is a major risk factor for shoulder dystocia, it has not been possible to accurately predict shoulder dystocia by attempting prediction of macrosomia.
image to view larger image
Next to macrosomia, the factor most
closely associated with shoulder dystocia is maternal diabetes
in pregnancy. One of the first clear-cut demonstrations of
this was Acker's 1985 paper showing the following:
Estimated fetal wt.
% shoulder dystocia
% shoulder dystocia
|< 4000 g
|> 4500 g
As can be seen, babies of diabetic
mothers had a three to fourfold increase in the risk of
shoulder dystocia compared to babies of nondiabetic mothers in
each weight category.
Although diabetic mothers accounted
for only 1.4% of the birth population in this study, they
accounted for 4.9% of shoulder dystocias. Acker also showed
that although the general rate of Erb palsy following shoulder
dystocia is roughly 10%, 17% of babies born to diabetic
mothers developed Erb palsy.
Other investigators have shown similar
or larger correlations between diabetes and shoulder dystocia.
In Al-Najashi's study (1989), the rate of shoulder dystocia in
babies weighing over 4000gm born of diabetic mothers was
15.7%. Babies born to nondiabetic mothers had a shoulder
dystocia rate of 1.6%.
Casey (1997), in a study of over
62,000 patients, found the shoulder dystocia rate in his
general obstetrical population to be 0.9% while in his
patients with gestational diabetes it was 3%.
Sandmire (1988) found a relative risk
for shoulder dystocia in the babies of diabetic mothers of 6.5
compared to nondiabetic mothers.
There are two main reasons for this
correlation between diabetes and shoulder dystocia. In the
first place, diabetes in pregnancy shows a very strong
correlation with macrosomia. The growth of diabetic babies
represents not only their genetic potential for growth but
also reflects the laying down of extra glucose substrates
present in both the mother and baby. Secondly, as previously
mentioned, the nature of the fetal growth differs in diabetic
babies. Growth is not as evenly distributed between the head
and trunk as it is in nondiabetic babies. Rather, babies of
diabetic mothers show a pattern of greater shoulder, chest,
and abdominal growth. As Ellis summarized in 1982:
"The infant of a diabetic mother has a
different body configuration than the infant of a nondiabetic
mother. Increased deposition of fat in various organs may be
due to increased insulin secretion in response to
Can shoulder dystocia be predicted in
babies of diabetic mothers?
In the 1980s several authors published
studies purporting to show that they could predict which
babies of diabetic mothers would be at high risk for shoulder
Elliott (1982) claimed that by
evaluating the chest-biparietal diameter in infants of
diabetic mothers weighing more than 4000 g, he could reduce
the incidence of traumatic morbidity at delivery from 27% to
Tamura (1986) found that in diabetic
women fetal abdominal circumference values greater than the 90
percentile correctly predicted macrosomia in 78% of cases. In
his study, when both the abdominal circumference and the
estimated fetal weight exceeded the 90th percentile in
pregnant women with diabetes, macrosomia was correctly
diagnosed 88.8% of the time.
Mintz, in a promising study from 1989,
published data showing that in his hands a combination of
fetal abdominal circumference > the 90th percentile for
gestational age and shoulder soft tissue width greater than 12
mm was the best predictor of macrosomia. His data reported a
sensitivity of 96%, specificity of 89%, and
"accuracy" -- positive predictive value -- of 93%. He also found a
significant correlation between shoulder width and a high
HgA1C, a blood test that measures blood sugar control over the
preceding three months.
Unfortunately, these results have not
been supported or replicated by other investigators. Multiple
experts in the field of shoulder dystocia have published data
from very large series that absolutely contradict the
conclusions listed above. In addition, the results of these
studies are not as powerful as might first be assumed.
In Elliott's study, for instance,
although he was able to show that a large number of babies
meeting certain chest-biparietal diameter criteria were
macrosomic, 39% of babies with these same parameters -- chest/biparietal
diameter ratio of > 1.4 -- were not larger than 4000 g. In
Tamura's steady, although he was able to predict macrosomia in
babies meeting certain abdominal circumference criteria, he
still was unable to identify the vast bulk of macrosomic
fetuses. As for Mintz's study, no one has yet been able to
duplicate his results.
In fact, most past studies have found that neither macrosomia nor shoulder dystocia can be reliably predicted in the babies of diabetic mothers. Acker (1985) showed that by using the criteria of large baby and diabetic mother he could predict 54.7% of shoulder dystocias -- but would miss 45.3% of them (false negatives). Delpapa (1991) stated that the predictive value of estimated fetal weight in babies of diabetic mothers for predicting shoulder dystocia was not sufficient to reliably identify them.
Moreover, most diabetic mothers do not
have macrosomic babies and the overwhelming majority of
macrosomic infants are not babies of diabetic mothers. The
bottom line is that macrosomia is as difficult to predict in
diabetic mothers as it is in the nondiabetic population.
There are two other studies of
interest relating to this question.
Coen (1980) showed that although
HgbA1C is a good marker for long-term monitoring of blood
sugars in diabetic patients, it is not a good predictor of
large-for-gestational age infants. The average HgA1C in
mothers of large-for-gestational age infants in his study was
6.7; for mothers delivering normal sized babies the average
HgA1C was 6.5 -- too close to be clinically useful.
Casey (1997) reported that although
the rate of shoulder dystocia was in fact increased in mothers
with gestational diabetes, this was not manifest in an
increase in the rate of Erb palsy.
The bottom line: Predicting macrosomia and shoulder dystocia in diabetic mothers has been as difficult as predicting these factors in the nondiabetic population.
3. Maternal weight gain
The data linking maternal weight gain
and fetal birth weight are controversial.
Abrams (1995) and Langhoff-Roos (1987)
both showed that total maternal weight gain was significantly
correlated with infant birth weight. Dawes (1991), however,
was not able to confirm this:
There was no apparent difference in
correlation between maternal weight gain and birth weight
between women giving birth to average for gestation or large
for gestational age infants
Moreover, several investigators have
reported conflicting information as to the effect of patterns
of maternal weight gain on ultimate fetal weight. Some studies
have found second trimester weight gain to be the major
determinate whereas others have found that the weight gain in
the last trimester was the most important factor. Given the
contradictory and confusing data on this subject, Dawes'
(1991) closing statement is probably the most apt:
"The variations in total (maternal)
weight gain and incremental weight gain are so wide that these
measurements are unlikely to be clinically useful."
4.. Fetal sex
There is little data correlating fetal
sex with macrosomia and shoulder dystocia. Although on average
male babies do weigh slightly more than females, there is no
data showing a significantly higher number of macrosomic male
infants than female infants.
Resnick in his classic 1980 paper
mentions fetal sex as a potential factor but does not supply
data to substantiate his claim. El Madany (1990) showed that
59.2% of babies experiencing shoulder dystocia in his study
were male -- statistically significant but not of much value as a
Any relationship thus far observed
between multiparity and either macrosomia or shoulder dystocia
has been linked to the fact that multiparous women are, on
average, older and heavier than primigravida women. They are
therefore more likely to have larger babies and are more
likely to have or develop diabetes, both of which would
increase the risk of shoulder dystocia. In addition, by
definition multiparous women have already had one or more
babies. Thus they may already have experienced a shoulder
dystocia which of course would place them at greater risk for
recurrent shoulder dystocia.
The only primary association between
multiparity and shoulder dystocia is the fact that multiparous
women are more likely than primiparous women to have
precipitous labors. This has been linked by several
investigators (Gonen , Acker ) to an increased
risk of shoulder dystocia.
Even though fetal growth slows in the
last several weeks of pregnancy, there is still some growth as
long as pregnancy continues. Thus the longer the baby remains
in utero, the larger the baby will be -- and the greater the risk
of shoulder dystocia. Acker (1985) was one of the first to
demonstrate this association. Chervenak confirmed this in 1989
when he reported that 25.5% of babies delivering at 41 weeks
gestation were macrosomic while only 6% (risk ratio 4.2) were
macrosomic in a group delivering between 38 and 40 weeks
gestation. Hernandez (1990), too, found a direct correlation
between post date babies and an increased risk of shoulder
dystocia. He attributed this entirely to the increased
tendency of post-date babies to be macrosomic.
Multiple risk factors
The greatest risk for shoulder
dystocia occurs in those groups of women who have multiple
risk factors. An obese woman with a large pregnancy weight
gain and gestational diabetes will have a significantly
greater likelihood of having a macrosomic baby and shoulder
dystocia than will a woman who has just one of these risk
factors. The worst possible combination of risk factors would
be a mother with diabetes, an estimated large-for-gestational-age fetus, a prolonged second stage of labor,
and a forceps delivery (to be discussed below). The rate of
shoulder dystocia in such a situation approaches 40%.
Summary of antepartum risk factors
- Macrosomia and maternal diabetes are
the main risk factors for shoulder dystocia
- Predicting fetal weight is
- Other factors -- maternal weight gain,
fetal sex, and post dates -- are secondary risk factors. They do
indicate an increased risk for shoulder dystocia but they are
only relevant to the degree that they increase risk of fetal
- Since multiparity increases the
number of precipitous labors it may be a primary risk factor
for shoulder dystocia
Intrapartum risk factors
Various characteristics of labor and
delivery have been claimed to be useful in predicting whether
or not a given mother-baby pair will end up with a shoulder
dystocia and possible brachial plexus injury.
1. Instrumental delivery
Several studies have clearly shown
that labors that end in instrumental vaginal
deliveries -- vacuum or forceps -- show a higher rate of shoulder dystocia in each fetal weight group.
Nesbitit (1998), for example, reported
the following data:
SD % in unassisted births
SD % in instrumental
Baskett (1995) similarly showed a
tenfold increase of shoulder dystocia and a fivefold increase
in brachial plexus injury (BPI) with mid-forceps deliveries
Low forceps deliveries
Benedetti reported that in deliveries
with the combination of a prolonged second stage of labor and
a mid pelvic delivery there was a 4.6% rate of shoulder
dystocia -- compared to 0.4% when there was neither prolonged
second stage nor mid pelvic delivery.
McFarland (1986) showed that the
relative risk of brachial plexus injury was 18.3 for
midforceps deliveries and 17.2 for vacuum deliveries when
compared to unassisted vaginal deliveries.
Thus it is clear that deliveries
requiring instrumental assistance have a higher risk of
shoulder dystocia and brachial plexus injury. It is not clear,
however, that it is the instrumental deliveries themselves
that are to blame for these shoulder dystocias. It may well be
that the mother's inability to push the baby out without
assistance is due to fetal macrosomia or an altered
distribution of fat between the fetal head, chest, shoulders,
and abdomen -- themselves major risk factors for shoulder dystocia.
2. Experience of the deliverer
Since the safe resolution of a
shoulder dystocia involves specific obstetrical maneuvers and
since shoulder dystocias occur relatively infrequently, it
would seem that more experienced practitioners would have
better outcomes in these situations merely by virtue of having
seen more of them. Such an opinion would surely be voiced by
most obstetricians and experienced labor and delivery nurses.
However the data does not support this belief.
In the only study that has looked at
the experience of the deliverer in relation to shoulder
dystocia, that by Acker in 1988, the number of Erb palsies
following shoulder dystocia deliveries did not vary with
either the number of years a physician had been in practice or
the number of deliveries that physician performed. As Acker
Most clinicians hardly gain expertise
and confidence in the difficult
manipulations required to resolve
shoulder dystocia due to the rarity of the condition.
3. Labor abnormalities
Several studies have shown a higher
incidence of shoulder dystocia in labors in which the second
stage of labor is prolonged. Nevertheless -- and
paradoxically -- shoulder dystocias are not infrequently seen
during labors with very rapid second stages.
Al-Natasha (1989) found that a delay
in the second stage of labor and slowed descent of the fetal
head in an obese multiparous woman greatly increased the
possibility that a shoulder dystocia would occur.
Hopewood (1982) found that there was a
deceleration phase of active labor from eight to 10 cm in 58%
of shoulder dystocia deliveries.
Acker (1985) showed that arrest
disorders significantly increase the chance of shoulder
dystocia with larger babies
But the literature has sometimes
contradicted itself on this issue.
Acker, in that same 1985 article
referenced above, states:
No particular labor abnormality was
predictive of an increased incidence of shoulder dystocia
relative to that encountered with a normal labor pattern, a
spontaneous delivery, or both.
Lurie (1995) also found no correlation
between length of the stages of labor and shoulder dystocia.
He showed that there was no difference in (1) the mean rate of
dilatation, (2) the percentage of protracted labors, or (3)
the mean duration of the second stage of labor in a group of
mothers who experienced shoulder dystocia deliveries versus a
group that delivered without complication. His conclusion was
that protracted labor did not seem to be a risk factor for
shoulder dystocia. As he says in his paper,
One could not identify shoulder
dystocia in advance while analyzing the rate of cervical
dilation or duration of the second stage of labor.
Hernandez (1990) reported that
although there is a relationship between the length of various
stages of labor and shoulder dystocia, 70% of patients who
experienced shoulder dystocia had normal labor patterns.
McFarland (1975) likewise reported the
same rate of labor abnormalities of the active phase of labor
and of the second stage of labor in both shoulder dystocia and
control groups. He concluded that labor abnormalities could
not serve as clinical predictors for the subsequent
development of shoulder dystocia.
Even if disorders of labor were found
to be correlated with shoulder dystocia, it is not clear
whether this would represent an independent risk factor. It
might merely confirm that labor disorders are more common with
macrosomic babies and that macrosomic babies more commonly
experience shoulder dystocia. To date there has been no major
study evaluating the length of various stages of labor broken
down by weight category in relationship to shoulder dystocia
To further complicate the issue, it is
well known that shoulder dystocias and brachial plexus
injuries are often seen with short second stages of labor:
Gonen (2000) reported that 7 of 17
patients (41%) with brachial plexus injury had second stages
of labor shorter than 10 minutes
Acker (1988) found that 31.8% of all
babies with Erb palsy were born after precipitate second
stages of labor. As he explains,
The rapidity of descent may prohibit
the fetal shoulders from entering the inlet in an oblique diameter,
preclude adequate preparation for delivery, and add to nerve root trauma.
This phenomenon of shoulder dystocias
with rapid second stages of labor will be discussed in further
4. Oxytocin and anesthesia
There does not appear to be any
independent correlation between the use of either oxytocin or
anesthesia and shoulder dystocia deliveries.
Oxytocin is generally used to increase
the strength of uterine contractions. To the extent that
oxytocin is used more frequently with macrosomic infants, it
might have a secondary correlation with shoulder dystocia
deliveries. But there is no published data linking oxytocin
use with the incidence of shoulder dystocia independent of
Likewise with anesthesia, there is no
reported increase in shoulder dystocia deliveries in labors in
which conduction anesthesia is employed.
There is no statistically significant
relationship between the absence of episiotomy, the frequency
of shoulder dystocia, and any subsequent neonatal injury. That
this is the case is perplexing given that almost all protocols
for the resolution of shoulder dystocia advocate making a
"generous episiotomy". This recommendation appears to be
without support in the literature.
There are two possible reasons one
might make an episiotomy in the case of a shoulder dystocia.
The first would be to make more room
for the baby to emerge. In this situation the indications for
making an episiotomy would be the same as in any delivery:
alleviating soft tissue dystocia of the perineum. If the
perineal tissue were tight, then an episiotomy might be
helpful in delivering the baby. However, if the soft tissue is
pliable and stretches easily, as in most multiparous women,
then an episiotomy will not make it any easier to free the
anterior shoulder from behind the pubic bone.
The second possible indication for an
episiotomy during a shoulder dystocia would be to allow more
room for the obstetrician's hand to move inside the pelvis in
performing the Wood screw maneuver or in attempting to deliver
the baby's posterior arm. An episiotomy might be helpful in
accomplishing these maneuvers in a woman whose perineal
tissues impede access to the fetal shoulders. However, in a
woman in whom the perineal tissues are lax enough to allow
these maneuvers to be performed, the automatic making of an
episiotomy will not facilitate delivery and would be
Thus the almost universal
recommendation that an episiotomy be made during a shoulder
dystocia delivery is not only without literature support, but
is theoretically unsupportable as well.
So, can shoulder dystocia be reliably
Up until this year, both the short and the long answer to this question would have been: "No". Nowhere in the literature were there studies that showed that the sensitivity or positive predictive value for predicting shoulder dystocia was high enough to justify interventions. While macrosomia, diabetes, prolonged second stage of labor, instrumental delivery, and other factors do indicate a statistically increased risk of having a shoulder dystocia, their low positive predictive value and high false positive rate make them clinically useless as tools for predicting -- and hence trying to prevent -- shoulder dystocia.
Below are the thoughts of various shoulder dystocia investigators on the predictability of this entity based on evidence that had been available up until this year (2006):
The profile of risk for shoulder
dystocia -- prolonged pregnancy, prolonged second stage of labor, macrosomia, and
assisted mid pelvic delivery -- were not clinically useful because the
large majority of cases of shoulder dystocia occur in patients without
these risk factors.
Most babies with shoulder dystocia do
not have risk factors.
Most of these preconception and
prenatal risk factors have extremely poor positive predictive
values and therefore do not allow the obstetrician to
accurately and reliably predict the occurrence of shoulder dystocia.
Only 25% of shoulder dystocia cases
had at least 1 significant risk factor . . . the positive
predictive value of pre-partum risk factors for shoulder dystocia is less than
2% individually, 3% when combined.
Hope for the future
As mentioned above, there is new research that has linked maternal size and fetal weight to the risk of shoulder dystocia. In addition, Dr. Emily Hamilton and her team of researchers in Montreal have developed a tool, based on sophisticated statistical and mathematical analysis of large numbers of shoulder dystocia cases, that can identify the majority of those mothers and fetuses destined to experience a shoulder dystocia.
The factors involved in this analysis of risk are maternal height, maternal weight, parity, gestational age, baby’s estimated weight, and maternal history of gestational diabetes or previous shoulder dystocia. Dr. Hamilton’s formula has been tested against several large independent samples of patients who had experienced shoulder dystocia with permanent injury. The data—some already published, some in the process of submission—shows that it is possible to consistently identify 50-70% of patients destined to have a shoulder dystocia with a false positive rate (rate of additional cesarean sections) of only 2.7%. (Dyachenko, Hamilton 2006)
Dr. Hamilton’s shoulder dystocia risk prediction tool has been commercialized into a web-based application by LMS Medical Systems and labeled CALM Shoulder ScreenTM (patent pending -- see www.lmsmedical.com).
dystocia and brachial plexus injury be prevented?
Up until this point we have been
looking for various ways of predicting which babies and which
labors will experience shoulder dystocia and possible brachial
plexus injury. But such predictions, even if they can be made,
are useless if there is no way to alter labor and delivery
management so as to prevent shoulder dystocia and
brachial plexus injury from occurring. Thus a most important
question is this: Given what we know about shoulder dystocia
and brachial plexus injury, is there anyway to prevent them?
As with the question of the predictability of shoulder dystocia, the answer to the question as to whether or not shoulder dystocia can be prevented has changed with the work of Gudmundsoon (2005) and Mazouni (2006) linking maternal size and fetal weight with shoulder dystocia and with the development of Hamilton’s shoulder dystocia risk predictive tool. Certainly if 50% or more of shoulder dystocias can be accurately predicted with a low false positive rate (2.7%), then prophylactic cesarean section for those patients thus identified becomes a reasonable preventive strategy. As further experience with the shoulder dystocia screening tool accumulates, this may well become the standard of care for attempting to prevent shoulder dystocia.
Up until this 2006, however, this tool had not been available. Let us look, therefore, at what information obstetricians have had up till now concerning the preventability of shoulder dystocia.
From the options available to
obstetricians for intervening in pregnancy, labor and delivery, the only
possible means for preventing shoulder dystocia would be:
- To perform elective
cesarean sections for suspected macrosomia
- To induce labor in
pregnant patients before their due dates in hopes of
preventing babies from becoming macrosomic
- To attempt through diet or
blood sugar control to limit maternal weight gain
There are some authors who have always felt that shoulder dystocia could be prevented. O'Leary, in his
book on shoulder dystocia, states:
obstetrician or midwife can anticipate this problem
[shoulder dystocia] as a result of routinely identifying
those risk factors that predispose to shoulder dystocia.
Thus prevention requires identification of risk factors,
which leads to anticipation of the problem . . .
Identification of critical risk factors will lead to
anticipation, which in turn will lead to prevention.
O'Leary then boldly goes on
The presence of macrosomia
of 4500 g alone is justification for cesarean section in
nonobese women. The presence of macrosomia of 4000-4500 g
may in itself be sufficient to warrant abdominal delivery
when other risk factors, especially a platypoid (flat)
pelvis, diabetes and/or obesity, are present.
But despite the certitude of
his statements, O'Leary presents no data to support his
Other authors have also tried
to articulate guidelines for avoiding shoulder dystocia.
Anchor (1988) has said:
We advocate the abdominal
mode delivery for infants of diabetic gravidas whose best
estimated fetal weight exceeds 4000 g.
Langer (1991) stated that if
all infants of diabetic mothers who weighed 4250 g or more
were delivered by cesarean section, the overall cesarean
section rate would increase by only 0.26% while shoulder
dystocia would be reduced by 76%. He goes on to acknowledge,
however, that in the nondiabetic group there is no weight that
provides an optimal threshold for cesarean section to avoid
But statements such as these have represented the far fringe of obstetrical opinion. It has been the consensus of the vast majority of obstetricians who have studied the subject that there was no real way to figure out which babies are likely enough to have shoulder dystocia to warrant changes in the management of their labors. The basic issue is this: One can suspect shoulder dystocia all one wants. But is there some combination of factors that predicts shoulder dystocia with an accuracy great enough to make doing cesarean sections, performing early inductions, or making other changes in management a reasonable course of action? The answer up until now has been "No." Below is listed evidence that has supported this conclusion:
Basket (1995) : The profile
of risk for shoulder dystocia -- prolonged pregnancy,
prolonged second stage of labor, macrosomia, and assisted
mid-pelvic delivery -- were not clinically useful because
"the large majority of cases of shoulder dystocia occur in
patients without these risk factors"
Resnick (1980): Most babies
with shoulder dystocia do not have risk factors. "The
diagnosis will often be made only after delivery of the
Gherman (2002): "Most of
these preconception and prenatal risk factors have extremely
poor positive predictive values and therefore do not allow
the obstetrician to accurately and reliably predict the
occurrence of shoulder dystocia."
Lewis (1998): Only 25% of
shoulder dystocia cases had at least 1 significant risk
Acker's (1986) : Almost
half (47.6%) of all shoulder dysoticas occurred in babies
weighing less than 4000 g.
Cunningham, author of
Williams Obstetrics, reports that 99.5% of babies
weighing 4000-4500 gms had a safe vaginal delivery without
Al-Najashi (1989) stated
that 41% of shoulder dystocia deliveries occurred in infants
of average birth weight, that is 2500 to 3999 g.
Eckert (1997): The greatest
number of injuries occurred in nondiabetic patients with
birth weights of less than 4000 g.
It is certainly clear that
there are risk factors which do increase the odds of shoulder
dystocia and brachial plexus injury occurring. But so many
babies with each of these risk factors do not encounter
shoulder dystocia and brachial plexus injury that it is
difficult to justify changes in management of all labors on
the basis of these suspicions.
Despite his statements in his
1992 book, even O'Leary, in a 1990 paper, acknowledges the
unpredictability of shoulder dystocia: He lists multiple risk
factors for shoulder dystocia -- and then goes on to prove
that the majority of macrosomic babies do not have these
The entire issue is best
summed up in Practice Bulletin #40 "Shoulder Dystocia" (2002)
by the American College of Obstetricians and Gynecologists.
They find the preponderance of current evidence consistent
with the following positions:
3. Most cases of shoulder
dystocia cannot be predicted or prevented because there are
no accurate methods to identify which fetuses will develop
4. Ultrasonic measurement
to estimate macrosomia has limited accuracy
5. Planned cesarean section
based on suspected macrosomia is not a reasonable strategy
6. Planned cesarean section
may be reasonable for the nondiabetic with an estimated
fetal weight exceeding 5000 g or the diabetic whose fetus is
estimated over 4500 g
Up until this year, the vast bulk of the medical literature continued to support these contentions. However given the new work of Hamilton and her co-workers, these statements may have to be re-evaluated over the next several years.
Would elective cesarean section for
suspected macrosomia be a reasonable strategy for decreasing
the number of shoulder dystocias and brachial plexus injuries?
Many papers have been written
trying to assess the utility of performing cesarean sections
for suspected macrosomia in an attempt to reduce the risk of
shoulder dystocia and permanent brachial plexus injury.
Gonen (2000) studied the use
of physical examination and ultrasound during labor to
identify babies suspected of being greater than 4500 g. His
goal was to see if by performing cesarean sections in these
cases he could reduce the rate of permanent brachial plexus
injury. Macrosomia was suspected in 47 cases -- but was only
confirmed at cesarean delivery in 21 of these (45% positive
predictive value). Thus there were 26 unnecessary cesarean
sections due to a false diagnosis of macrosomia. Moreover,
over 84% of the macrosomic babies born from his subject
population were missed. Of the 115 cases of macrosomia, only
21 were correctly identified in labor -- a dismal sensitivity
rate of 18.3%. Of the 17 babies that developed brachial plexus
injuries in his study, three were macrosomic -- but they were
not identified prior to or during labor! The remaining 14
injured babies were not macrosomic. Thus, Gonen's attempt to
decrease the brachial plexus injury rate by performing
cesarean sections on suspected macrosomic babies missed most
big babies and resulted in many unnecessary cesareans. He
confirmed what is a major problem with any attempt to predict
and prevent shoulder dystocia and brachial plexus injury:
The group in which they occur most often is that of normal
Many other studies have
resulted in similar conclusions:
Rouse and Owen (1999) showed
that prophylactic cesarean section would require more than
1000 cesarean sections and millions of dollars to avert a
single permanent brachial plexus injury.
Basket (1995) stated that if
in his series of patients all mid-forceps deliveries had been
replaced by cesarean sections, 3268 cesarean section
deliveries would have been performed to prevent 16
non-permanent brachial plexus injuries. Even if cesarean
sections were performed only for babies suspected of being
greater than 4500 g, 54 cesarean sections would have to be
performed to prevent one case of non-permanent brachial plexus
Eckert, in his 1997 paper,
sums up the problem neatly:
In practice, only estimates of fetal weight, not actual
weights, are available to practitioners seeking to predict
the risk of birth injury. Weights estimated before delivery,
whether by ultrasound or clinical estimation, are
notoriously inaccurate. Even if we were able to identify a
specific fetal weight that mandated cesarean section, any
scheme that relied on estimated fetal weight to risk
patients into cesarean delivery would result in the delivery
of many infants appreciably smaller than the estimated fetal
weight assigned them.
He points out that
The greatest number of
injuries occurred in nondiabetic pregnancies with birth
weights less than 4000 g. No protocol for managing
macrosomia recommends cesarean delivery for estimated fetal
weight of less than 4000 g.
In our opinion, the number
of cesarean sections necessary to prevent a single birth
injury in a normal glycemic population precludes our
recommending mandatory cesarean delivery at any weight
Delpapa (1991) studied
nondiabetic women thought on ultrasound to have macrosomic
fetuses. He concluded that he would have to do 76 cesarean
sections to prevent five cases of shoulder dystocia:
Our study does not support
the contention that elective cesarean section is justified
in those women with fetuses suspected to be macrosomic as a
means of preventing persistent infant mortality. A very
large number of unnecessary cesarean sections would be
performed without much preventive effect.
McFarland (1986) presented
data by weight group showing how many cesarean sections would
need to be performed to prevent even temporary brachial plexus
His conclusion is that even
if a reliable means of estimating fetal weight were possible,
by performing cesarean sections for all babies estimated to be
greater than 4500 g only 32% of all shoulder dystocias would
be avoided. At any lower weight cut off, there would be far
too many cesarean sections for far too little gain.
Rouse also tried to quantify
the effectiveness of a policy of elective cesarean section for
ultrasound-diagnosed fetal macrosomia. He found that in women
without diabetes, if a cesarean section were performed for
each baby with a suspected weight of greater than 4500 g, 3695
cesarean sections would have to be performed at an additional
cost of $8.7 million for each permanent brachial plexus injury
Bryant (1998) data showed
that even assuming ultrasound diagnosis to be accurate in
predicting fetal weight, between 155 and 588 cesarean sections
would have to be performed to obviate a single case of
permanent injury, depending on the weight cut-off selected:
Our data show that a policy
of elective cesarean delivery in cases of suspected fetal
macrosomia had an insignificant effect on the incidence of
brachial plexus injury. Although the contribution of this
policy to the cesarean delivery rate was small, the number
of cesarean deliveries required to prevent a single case of
permanent brachial injury was high and probably
Gregory (1998) stated that if 5.5% of all brachial plexus
injuries were permanent -- which his data demonstrated -- only
one in 3833 macrosomic infants would have a persistent Erb
palsy. Moreover, he found that one half of all of the
shoulder dystocias in his series occurred in normal weight
Kolderup (1997) found that a policy of elective cesarean
section for macrosomia would necessitate 148 to 258 cesarean
sections to prevent a single persistent injury. He feels
that "these findings support a trial of labor and judicious
operative vaginal delivery for macrosomia infants."
Sandmire (1993) discusses the difficulty in attempting to
determine fetal size in utero:
Any approach using ultrasound would have to demonstrate that
its use improves newborn or maternal outcome without
disproportionate increases in morbidity and mortality. A barrier to achieving
this goal is the inaccuracy associated with estimation of fetal
weight. The current ultrasonic procedures for estimation of fetal weight are not
accurate enough for detecting macrosomia defined by weight criteria.
And even if clinicians could determine fetal weight
accurately, the frequency of persistent fetal injuries associated with
vaginal birth of the macrosomic fetus is so low that induction of labor or
birth is not justified on that basis. Delivery decisions
based on inaccurate
estimated fetal weights should be avoided.
He also composed a chart drawn from data in several other
studies in which he evaluated the rate of permanent brachial
plexus injuries and the number of cesarean sections that
would be necessary to avoid them:
C/S to prevent BPI injuries
C/S to prevent permanent
Sandmire (1996) concludes that a policy of employing
cesarean section for suspected macrosomia in hopes of
preventing permanent brachial plexus injury will not work
1. The inaccuracy of ultrasound in estimating fetal weight
2. The increases in morbidity and mortality that would occur
from the very large numbers of cesarean sections so
3. The many cesarean sections would have to be done to
prevent one significant fetal injury
Sandmire also takes care to distinguish minor injuries, such
as clavicular fracture and transient brachial plexus injury,
from severe persistent fetal injuries. He admonishes anyone
considering the issue of cost vs. benefit in the management
of suspected macrosomia to make decisions based only on
significant fetal injuries, such as permanent brachial
plexus injuries and severe neurologic damage.
Summarizing, the major conclusion of most of the obstetrical
literature discussing the strategy of performing cesarean
sections for suspected macrosomia is that it would not be
practical because it would require far too many unnecessary
interventions for the benefits that would be obtained.
Cesarean sections are not without risk, especially for
diabetic and/or obese women
Although cesarean section is one of the most commonly
performed operations in the United States, it still carries
much greater risk than does a vaginal delivery. These risks
include blood loss, infection, damage to other pelvic
organs, and respiratory emergencies. Moreover, the recovery
period is longer and more painful and performing one
cesarean section greatly increases the likelihood that a
woman will have her next baby by cesarean section as well.
Finally, total hospital care for women delivering a baby via
cesarean section is 50%-100% more expensive than the cost of
a vaginal delivery.
Thus in order to justify the increased risk, pain, and
expense of performing cesarean section in hopes of avoiding
shoulder dystocia and permanent brachial plexus injury,
there has to be substantial evidence that this is an
effective policy. As has been shown, such evidence has up until now been lacking. In fact, the evidence has been contrary to this supposition.
What about early inductions as a means of avoiding shoulder
dystocia and brachial plexus injury?
Many have thought that by cutting off one to two weeks of
growth of a fetus at term, a baby might be delivered small
enough to avoid shoulder dystocia and the risk of permanent
brachial plexus injury. The problem with this theory is that
there is no data to support it.
In the first place, the growth rate of babies differs
significantly, both between babies and at various points in
pregnancy for each baby. Thus it is impossible to estimate
how much additional growth is prevented by "early delivery".
Most importantly, studies looking at this means of
attempting to prevent shoulder dystocia have never been
successful in reducing the number of macrosomic babies or
showing that such a program reduces the risk of shoulder
Del Papa (1991) found that early induction did not decrease
Gonen (1997) randomized patients suspected of macrosomia
based on ultrasound examination to an early induction
group -- 134 patients -- or a routine pregnancy follow-up
group -- 139 patients. There was no statistically significant
difference in shoulder dystocia between the two groups.
Several authors -- Leaphart (1997), Friesen (1995), Combs
(1993) -- have even shown that this approach of early induction
actually increased the cesarean section rate with no
decrease in the incidence of shoulder dystocia.
So, can shoulder dystocia be prevented?
A review of the literature indicates that the answer to this question has up until this year been "No." Estimates of fetal weight are unreliable. It is impossible to accurately tell which babies will be macrosomic. And it has previously been impossible to reliably determine which babies will develop shoulder dystocia. Based on previous information available to obstetricians, a policy of prophylactic cesarean section would have required huge numbers of operations to prevent a single case of permanent brachial plexus injury. It is also the case that a policy of elective induction has not been shown to decrease the number of shoulder dystocias.
Hope for the future
As has been discussed, there is now published research, based on sophisticated statistical and mathematical analysis of a large numbers of shoulder dystocia cases, that shows that it is possible to identify 50% or more of those mothers and fetuses at highest risk for shoulder dystocia.
Dr. Emily Hamilton and her team of researchers in Montreal have developed a formula considering maternal height, maternal weight, parity, gestational age, estimation of baby’s weight, and maternal history of gestational diabetes or previous shoulder dystocia that, when tested against several large independent samples of patients who had experienced shoulder dystocia with permanent injury, consistently identified 50-70% of them with a false positive rate (rate of additional cesarean sections) of only 2.7%. (Dyachenko,Hamilton 2006 and subsequent unpublished data). This tool has been commercialized into a web-based application by LMS Medical Systems and labeled the CALM Shoulder ScreenTM (patent pending) -- see www.lmsmedical.com) for more information.
As this probabilistic tool becomes more widely utilized, it may well be possible to prevent a significant proportion of brachial plexus injuries by recommending prophylactic cesarean section to those women identified as being at high risk for shoulder dystocia.
dystocia be resolved without fetal injury when it does occur?
The evidence from the literature
on shoulder dystocia shows clearly that:
(1) Shoulder dystocia
cannot be predicted with any degree of accuracy and
(2) Shoulder dystocia
cannot be prevented by any specific strategies or maneuvers.
The question thus arises "How
should shoulder dystocia be handled when it does occur? Can it
successfully be resolved without injuring the baby or the
Much has been written on this
subject. Multiple maneuvers claiming to be able to resolve
shoulder dystocia have been described. We will now take a look
at what these maneuvers are, how they work, and how effective
they really are.
The first step in treating
shoulder dystocia is recognizing when it occurs.
There are two main signs that
a shoulder dystocia is present:
(1) The baby's body does
not emerge with standard moderate traction and maternal
pushing after delivery of the fetal head.
(2) The "turtle sign". This
is when the fetal head suddenly retracts back against the
mother's perineum after it emerges from the vagina. The
baby's cheeks bulge out, resembling a turtle pulling its
head back into its shell. This retraction of the fetal head
is caused by the baby's anterior shoulder being caught on
the back of the maternal pubic bone, preventing delivery of
the remainder of the baby.
photo by Kristina Kruzan, www.dynamicdoula.com
Traction: "Excessive" or
Babies rarely fall out of the
pelvis -- nor should they. Especially in an age where
conduction anesthesia (epidurals, spinals) is used routinely,
often a mother must push several times in order to deliver the
remainder of her baby after its head has been born. To
facilitate the passage of the baby's anterior shoulder under
mother's pubic bone, it is standard practice for the deliverer
to deflect the baby's head downwards and to apply traction
while the mother is pushing.
It is often said --
especially in court rooms -- that traction should never be
applied to the fetal head during delivery. This is certainly
not the case -- and is absolutely not the standard of care
practiced by obstetricians across the United States. Such
assisting of delivery of the head is necessary and is approved
obstetrical practice as can be seen in any textbook of
What about the slippery term
"excessive force"? This term conveys an image of an
obstetrician pulling with all his or her might, propping a leg
against a delivery table for support, etc. Students of
shoulder dystocia have long sought to determine exactly what
degree of force constitutes "excessive force". Some
investigators, such as Allen (1991) and Gonik (2000), have
even tried to determine this by using specially-constructed
gloves with piezoelectric fingertip sensors to measure
pressures at delivery.
It would seem on the face of
it that the use of strong forces to attempt to deliver an
impacted shoulder should be universally condemned. But one
must take into account the circumstances involved. There are
times when all maneuvers have been attempted to resolve a
shoulder dystocia and when the only options left are either a
maximal effort to extract the baby, including greater than
desired forces, or fetal death. In such cases, faced with the
ultimate catastrophe of the death of a baby, the risk of
brachial plexus or other fetal injury must be accepted.
What the physician must
not do when a shoulder dystocia occurs is to lose
composure. Most shoulder dystocias occur unexpectedly. But by
restraining panic, keeping a cool head, and employing a
previously thought-out set of maneuvers, almost all shoulder
dystocias can be resolved with excellent results for both baby
and mother. The term "almost all" is used advisedly as
sometimes, even in the most expert hands, and even with
relatively mild shoulder dystocias, fetal or maternal injury
What to do when a shoulder dystocia
Several things should be done
as soon as a shoulder dystocia is recognized. The obstetrician
should ask to have a second obstetrician called and should ask
the nurses to make sure that extra personnel are available.
The obstetrician should also stay informed of the time that
has elapsed since delivery of the head. One means of doing
this is to designate someone to call out the time since
delivery of the head at fixed intervals -- perhaps every 30
seconds. Pediatric or neonatal assistance should be called so
as to be available to evaluate and potentially resuscitate the
baby after delivery. Anesthesia staff should be summoned. One
person should be designated as a note taker to record the
timing of events.
Once a shoulder dystocia is
recognized, there are several specific obstetrical maneuvers
that have been proven to be of benefit in assisting in the
resolution of the dystocia.
McRoberts maneuver and
The first two maneuvers
generally attempted in order to resolve a shoulder dystocia
are (1) McRoberts maneuver and (2) suprapubic pressure. In
fact both of these maneuvers are so benign and so effective
that they are sometimes employed prophylactically in
anticipation of a potential shoulder dystocia.
image to view larger image
McRoberts maneuver is named
for William A. McRoberts, Jr. who popularized its use at the
University of Texas at Houston. It involves sharply flexing
the legs upon the maternal abdomen. By doing this, the
symphysis pubis is rotated cephalad and the sacrum is
straightened. In a high percentage of cases this by itself
suffices to free the impacted anterior shoulder.
Suprapubic pressure is the
attempt to manually dislodge the anterior shoulder from behind
the symphysis pubis during a shoulder dystocia. It is
performed by an attendant making a fist, placing it just above
the maternal pubic bone, and pushing the fetal shoulder in one
direction or the other. Since shoulder dystocias are caused by
an infant's shoulders entering the pelvis in a direct
anterior-posterior orientation instead of the more physiologic
oblique diameter, pushing the baby's anterior shoulder to one
side or the other from above can often change its position to
the oblique which will allow its delivery. As mentioned above,
suprapubic pressure in conjunction with McRoberts maneuver is
often all that is needed to resolve 50-60% of shoulder
In order to show more clearly
how McRoberts maneuver aids in the resolution of a shoulder
dystocia, Gherman (2000) performed a study in which he took
x-rays of 36 women in the dorsal lithotomy position before and
after McRoberts positioning. He found that there were no
significant changes in the anterior-posterior and transverse
diameters of the pelvic inlet, midpelvis, and pelvic outlet.
There also was no increase in the obstetric, the true, and the
diagonal conjugates of the pelvis. Thus, McRoberts maneuver
does not change the actual dimensions of the maternal pelvis.
What was seen, however, was a rotation of the symphysis pubis
toward the maternal head that significantly changed the angle
of inclination between the top of the symphysis and the top of
the sacral promontory. This, in conjunction with the
flattening of the sacrum, is often enough to allow stuck fetal
shoulders to deliver.
A study by Gonik and Allen
(1989) confirmed that this is the case. They showed that
implementation of McRoberts maneuver can significantly reduce
required fetal extractive forces and brachial plexus
stretching in shoulder dystocias. In addition to allowing the
anterior shoulder to slide more freely under the back of the
symphysis, the flattening of the sacrum relative to the lumbar
spine allows the posterior fetal shoulder to more easily pass
over the sacrum and through the pelvic inlet.
How successful is McRoberts
maneuver? Gherman (1997) observed 250 shoulder dystocia
deliveries at USC from 1991 to 1994 and reported that
McRoberts maneuver alone was successful in resolving 42% of
them. Fifty-four percent of all shoulder dystocias were
resolved by a combination of McRoberts maneuver, suprapubic
pressure and/or procto-episiotomy without further maneuvers
being necessary. McFarland (1996) reported similar findings:
39.5% of shoulder dystocias resolved with McRoberts maneuver
alone while 58% resolved with a combination of McRoberts
maneuver and suprapubic pressure.
Although McRoberts maneuver
and suprapubic pressure are generally safe, it is possible to
cause maternal injury by performing them. Symphyseal
separations and transient femoral neuropathies from overly
aggressive hyperflexing of the maternal thighs have been
reported. However neither McRoberts maneuver nor suprapubic
pressure involves direct manipulation of the fetus, making it
unlikely that either of these procedures will injure a baby.
Wood's Screw maneuver
First described in the
literature in 1943, this procedure involves the progressive
rotation of the posterior shoulder in corkscrew fashion to
release the opposite impacted anterior shoulder. In its
classic description, pressure is applied on the posterior
shoulder's anterior surface. A variation of this -- the
Rubin's maneuver -- involves pushing on the posterior surface
of the posterior shoulder. In addition to the corkscrew
effect, pressure on the posterior shoulder has the
advantage of flexing the shoulders across the chest. This
decreases the distance between the shoulders, thus decreasing
the dimension that must fit out through the pelvis.
Delivery of the posterior
Another effective maneuver
for resolving shoulder dystocias is the delivery of the
posterior arm. In this maneuver, the obstetrician places his
or her hand behind the posterior shoulder of the fetus and
locates the arm. This arm is then swept across the fetal chest
and delivered. With the posterior arm and shoulder now
delivered, it is relatively easy to rotate the baby, dislodge
the anterior shoulder, and allow delivery of the remainder of
The major risk of this
procedure is that of fracturing the humerus. Gherman (1998)
reported 11 (12.4%) humeral fractures in 89 shoulder dystocias
resolved by delivery of the posterior arm. However, since
almost all humeral fractures heal quickly and without
permanent damage, this would appear to be a small price to pay
for the successful delivery of an infant in a life threatening
situation when other maneuvers have not worked.
There have been multiple
other techniques and procedures described over the years to
resolve shoulder dystocias. None of these, however, have
reached the level of "mainstream". Some of these are the
Zavanelli maneuver, deliberate fracture of the clavicle,
symphysiotomy, the "all-fours" maneuver, and fundal pressure.
Although almost certainly
performed by obstetricians and midwives in the past, this
maneuver was first attributed in the literature to Dr.
Zavanelli, an obstetrician in private practice in Pleasanton,
California, in 1977. Dr. Zavanelli reported that during one
difficult shoulder dystocia delivery, after having attempted
all other maneuvers, he finally resorted to flexing the fetal
head and pushing it back up into the vagina. By so doing, he
was able to get the fetal head back into the pelvis, perform
an emergency cesarean section, and deliver a live baby.
In this cephalic replacement
maneuver -- now generally referred to as the Zavanelli
maneuver -- the head must first be rotated back to its
pre-restitution position -- that is, occiput anterior -- and
then flexed. Constant firm pressure is applied while pushing
the head back into the vagina. Tocolytic agents or
uterine-relaxing general anesthesia may be administered to
facilitate this process. Cesarean section must be performed
immediately after replacement of the head.
The Zavanelli maneuver enjoys
a mixed reputation. O'Leary (1993) reported on 59 women who
had undergone replacement of the fetal head following
unsuccessful attempts at vaginal delivery. All but 6 of these
infants were successfully replaced and delivered by Cesarean
section. He therefore suggested that the Zavanelli maneuver
might not need to be used as a last resort maneuver but might
be considered if any undue difficulty were encountered with a
But a closer look at the data
he reports is less reassuring. In his series, the delay of
cephalic replacement following delivery of the head ranged
from 5 minutes to greater than 30 minutes. He was unable to
replace the fetal head in six instances and he reported
replacement as "difficult" in five. Apgar scores at 5 minutes
were less than 6 in 61% of these babies and were less than 3
in 27%. Four babies in his series had seizures in the nursery,
two had permanent neurologic injury, five experienced a
permanent Erb palsy, and two died. Three percent of the
mothers experienced ruptured uterus and 5% suffered uterine
Although Sanberg (1999)
reported a much more optimistic experience with the Zavanelli
maneuver, the data from O'Leary's large series is sobering.
While it is incumbent upon all obstetricians to know about the
Zavanelli maneuver and how to perform it when a difficult
shoulder dystocia occurs, its significant potential for fetal
and maternal injury must relegate it to the status of a "last
Deliberate fracture of the
Almost all detailed accounts
of shoulder dystocia include deliberate fracture of the
clavicle as one modality for resolving this situation. But
there are few accounts of this procedure actually being
performed. In practice, the clavicle poses a formidable
obstacle to its fracture. It is a significant bone, even in a
fetus. Although the fracture of the clavicle certainly would
decrease the transverse diameter of the chest and shoulders,
the potential of damaging the great vessels, fetal lungs, and
other structures make this an extremely hazardous procedure
even if it were possible to perform easily. In fact most
descriptions of transection of the clavicle involve fetuses
that are already dead and require the use of a large scissors
or other sharp instrument for cutting the clavicle.
Symphysiotomy is a procedure
that had been performed in the past and is now performed only
in areas remote from the ability to perform Cesarean sections
on a rapid basis. However it has enjoyed something of a
renaissance in the literature in recent years. The theory is
that by transecting the firm ligaments joining the left and
right symphyseal bones, an additional 2-3cm in pelvic
circumference can be gained. In most cases this will allow the
anterior shoulder to be delivered beneath the symphysis. The
benefit of the procedure is that it can be performed rapidly
-- it usually takes 5 minutes or less -- and can be done under
local analgesia. In subsequent pregnancies a woman who has
undergone a symphysiotomy has an intact uterus and a slightly
The symphyseal separation
obtained by symphysiotomy affects the transverse diameters of
the pelvis, particularly those of the mid cavity and outlet.
The area of the pelvic brim increases by 8% for every 1cm of
The technique involves
abducting the thighs to 80 degrees (but no further). A 2cm
skin incision is made over the mons. With an index finger in
the vagina displacing the urethra, the scalpel is inserted in
the midline of the mons at the junction of the upper and
middle thirds of the symphysis. If difficulty is experienced
finding the ligament, a needle can be placed first. The blade
is inserted until it impinges on the vaginal epithelium as
determined by the finger in the vagina. Using the upper
symphysis as a fulcrum, the knife is rotated, cutting the
lower 2/3rds of the symphysis. The knife is then turned 180
degrees and the upper third of the symphyseal ligament is
transected. Separation thus obtained is between 2 and 3cm --
the width of a thumb.
separation, the bladder must be drained for five days. The
patient is kept in bed on her side for three days. Sometimes
the knees are tied together to enforce this position. On the
fourth day the patient may sit in bed and on the fifth day
walk. Results in terms of maternal recovery are uniformly
excellent with return of full ambulation and pelvic stability.
The major risk is to maternal
soft tissues including the bladder and urethra. As with many
techniques, the more experience one obtains with procedure,
the more quickly it can be performed and the lower the
complication rate. Hartfield published a detailed description
of symphysiotomy in 1973 in order to remind obstetricians that
such a procedure exists. Although not advocating it in
developed countries as a first step, he does state that it can
be effected very quickly and may in some instances save a
fetus' life when all other measures to resolve a shoulder
dystocia have been exhausted. As he says in a second article
he published on the subject in 1986,
The risk of maternal soft
tissue trauma has to be weighed against the almost certain
loss of the baby if other methods of vaginal delivery are
In 1976, Ina May Gaskin
described a maneuver for the resolution of shoulder dystocia
that involves placing the gravid mother on her hands and
knees. (Bruner, 1998) used this procedure in 82 deliveries
complicated by shoulder dystocia and was able to resolve it in
68 cases (82%) with this maneuver alone. The average time
needed to move the mother into this position and to complete
delivery was reported to be 2-3 minutes. Unfortunately, there
was no detailed description of fetal and maternal outcome in
this report. Also, reports about this procedure have generally
been in the midwifery literature, involving a patient
population less likely to have epidural anesthesia and thus
more likely to be fully mobile.
It may be that the "all-fours
maneuver" is merely another means of changing the angle of the
symphysis in relation to the stuck shoulder, akin to McRoberts
maneuver. Since the all-fours maneuver involves a gravid woman
at the end of her pregnancy, exhausted by a long labor, often
with an epidural in place, being moved quickly out of her
delivery position onto all fours on her bed or on the floor,
the practicality of this maneuver for a general obstetrical
population is open to question. Unless more data is presented
as to its efficacy and utility, it cannot be considered a
standard procedure for the resolution of shoulder dystocia.
Which maneuvers should be performed
Many authors have proposed
various protocols of prescribed maneuvers for the resolution
of shoulder dystocia. Most are similar with only minor
When a shoulder dystocia is
recognized, it is generally agreed McRoberts maneuver and
suprapubic pressure should be implemented rapidly and
simultaneously. These by themselves will resolve more than
half of all shoulder dystocias. If the shoulder dystocia
persists, other maneuvers can be performed in any order.
These include the Wood's screw maneuver in either the
clockwise or counter clockwise direction, attempting to
deliver the posterior arm, and, in extremis, consideration of
such techniques as the Zavanelli maneuver or symphysiotomy.
ACOG, in its bulletin on
shoulder dystocia, proposed the following sequence of
maneuvers for reducing a shoulder dystocia:
1) Call for help -
assistants, anesthesiology, pediatrician. Initiate gentle
traction of the fetal head at this time. Drain the bladder
2) Generous episiotomy.
3) Suprapubic pressure with
normal downward traction on fetal head.
4) McRoberts maneuver.
Then, if these maneuvers
5) Wood's screw maneuver.
6) Attempt delivery of
Harris in a 1984 paper
recommended a similar protocol:
1) McRoberts maneuver.
2) Suprapubic pressure.
3) Large mediolateral
episiotomy if above steps fail.
4) Wood's screw maneuver.
5) Attempt to free
Gherman (1998) discussed the
protocol for managing shoulder dystocia utilized at that time
at the University of Southern California:
Wood's corkscrew maneuver
Posterior arm extraction.
Zavanelli maneuver or
symphysiotomy if all else fails.
McFarland (1996) reported
that the use of two maneuvers alone -- McRoberts and
suprapubic pressure -- resulted in the resolution of 58% of
276 cases of shoulder dystocia in his series. He found that
the addition of the Wood's Screw maneuver and delivery of the
posterior arm were sufficient to resolve the shoulder dystocia
in all remaining cases. He also found that there was a direct
correlation between the rate of brachial plexus injury and the
number of maneuvers employed to resolve the shoulder dystocia.
A second correlation he found was that as the fetal weight
increased, the number of maneuvers required to resolve
shoulder dystocias increased.
O'Leary, in his 1992 book,
presented a much more elaborate protocol. His first step was
to make a "truly adequate" episiotomy. He goes on to state
that the slow rate of decline of pH per minute after occlusion
of the umbilical cord -- 0.04units/min as reported by Wood
(1973) -- allows plenty of time to resolve the shoulder
dystocia in an organized manner. He distinguishes between
mild, moderate and severe shoulder dystocia and those that are
"undeliverable" and presented different delivery protocols for
Grade of shoulder dystocia
Treatment of shoulder
Mild shoulder dystocia
pressure, which can be directed either posteriorly or to
Rubin maneuver (reverse
of the Wood maneuver)
Moderate shoulder dystocia
delivery of posterior shoulder.
Hibbard technique -- pushing
back on the head to displace the anterior shoulder.
(Note: This is a unique recommendation. The Hibbard
maneuver is not generally considered a modern obstetrical
technique because it involves further potential stretching
of the brachial plexus and -- at least in the original
description -- Hibbard recommends fundal pressure as the
shoulder is sliding below the symphysis)
Severe shoulder dystocia
All of the
O'Leary feels that delivery of the posterior arm is "the most
efficacious and expeditious means of overcoming shoulder
Dignam comments similarly: "I
favor delivery of the posterior arm as the most efficacious
and expeditious means of overcoming shoulder dystocia". His
plan of action is as follows: Make a generous episiotomy,
avoid fundal pressure, pull the baby's posterior hand down
across the chest, and attempt to adduct the posterior shoulder
as Rubin discusses.
As has been shown, different
authors recommend different combinations of maneuvers in
attempting to resolve shoulder dystocias. But what every
author emphasizes, and what the ACOG bulletin stresses, is
that the most important aspect of resolving a shoulder
dystocia is for the obstetrician to have a clear-cut, well
thought-out sequence of maneuvers in mind when a shoulder
dystocia is encountered. The general consensus is that the
best results in resolving shoulder dystocias are obtained when
brachial plexus injury caused by shoulder dystocia?
(1) Recognizes the shoulder
(2) Knows the different
maneuvers involved in attempting to resolve shoulder
(3) Implements them in a
carefully controlled, calm, and organized fashion.
In his 2002 paper, Pecorari
states the following:
obstetricians and midwives, in court Erb palsy has been
causally connected with shoulder dystocia and errors in
management, although it is not always true. Perhaps the lack
of an obvious explanation has contributed to the
identification of the birth attendant as a handy scapegoat.
When there is a permanent brachial plexus injury following
shoulder dystocia, responsibility
for this injury is often presumed to be with the obstetrician
who supposedly did not foresee
that a shoulder dystocia was likely to occur or mishandled it
when it did. Yet a review of
the literature does not substantiate such assumptions. Gherman
in his 1998 paper summarizes the refutation to these claims:
We feel that some cases of brachial plexus injury are
unavoidable events. Recent reports have noted that brachial
plexus palsies occur:
(1) In the absence of
characteristic risk factors
(2) In the absence of shoulder dystocia
(3) In the posterior arm of infants whose anterior shoulder
was impacted behind the
(4) In vertex-presenting fetuses delivered by atraumatic
(5) Without apparent relationship to the type or number of
maneuvers used to disimpact the
(6) In association with other peripheral nerve injuries
(7) With electromyelographic evidence of muscular denervation
during the immediate
postpartum period [indicating pre-delivery injury].
Jennett commented in a
similar vein in 1997:
Evidence continues to accumulate that renders a univariate
theory of the causation of
brachial plexus injury untenable . . . Intrauterine maladaption
is responsible for some
instances of brachial plexus injury.
He notes that in his series of deliveries from 1977 to 1990,
22 of 39 (56%) brachial plexus
injuries were not associated with shoulder dystocia. In that
same paper he quotes Pearl
(1993) and Gimovsky (1995), both of whom reported brachial
plexus injuries in babies
delivered from the occiput posterior position without shoulder
dystocias. He further cites
Walle (1993) who observed in his patient population that 1/3rd
of 175 shoulder dystocias
involved the posterior shoulder.
There are many other similar reports:
Hardy (1981) reported 36 infants with brachial plexus injuries
of whom only 10 had shoulder dystocia noted at birth.
Gilbert (1990) initially published a study of 1000 infants
with brachial plexus injury in
which 39% did not have shoulder dystocia at delivery. In a
supplementary article in 1999,
he reported that 47% of babies with brachial plexus injury in
his now larger series
experienced deliveries in which no shoulder dystocia was
noted. Even among macrosomic
fetuses in this series, 26% of brachial plexus injuries
occurred in the absence of shoulder
Gram (1997) noted that only 8 babies had shoulder dystocia
deliveries in a group of 15 who
experienced brachial plexus injury. In the other seven cases,
there had been no birth
In Gonik's 1991 paper, 71% of all injured infants in his
series were the product of
deliveries without recognized shoulder dystocia.
Ouzounian (1997) reported 4 babies with brachial plexus injury
in which there was not even
downward traction during delivery.
In Hillard's (1997) series of babies with Erb palsy, 15 of 51
babies had not experienced
shoulder dystocia during delivery.
Sandmire (1996) reported 17 babies in his series of 36 with
brachial plexus injuries whose
deliveries did not involve shoulder dystocia. This article
included his personal review of
the literature concerning brachial plexus injury (BPI) with
and without shoulder dystocia:
deliveries greater than 4,500 grams
|BPI with shoulder dystocia
||BPI without shoulder dystocia
As can be seen, 51% of
brachial plexus injuries in over 1727 deliveries of macrosomic
did not involve shoulder dystocias.
What does cause brachial
The standard explanation for brachial plexus injury is that it
results from excessive
downward traction by the obstetrician on the fetal head during
the delivery of the anterior
shoulder. This supposedly overstretches the brachial plexus
thus injuring it.
It is in fact true that the majority of brachial plexus
injuries, whether permanent or not,
do follow shoulder dystocias. There also appears to be a
correlation between the severity
of the shoulder dystocia and the degree of brachial plexus
injury. But there is also much
evidence in the literature that brachial plexus injuries are
caused by factors other than
shoulder dystocia-related trauma.
What other than shoulder dystocia might cause brachial plexus
The tractor-trailer theory
Sandmire (2000) and others
have recently proposed an explanation for brachial plexus
injuries that explains much of the data that has been
collected over the years.
Obstetricians have long sought to understand the mechanism of
those brachial plexus injuries
that occur following extremely rapid second stages of labor,
some of which are as short as
one or two contractions. Sandmire studied what happens to the
various parts of the fetus
during uterine contractions and maternal pushing. He noted
that the forces of contractions
and maternal pushing act on the long axis of the fetus. If the
fetus's anterior shoulder
were to get stuck behind the maternal pubic bone and continued
pressure were applied to the
long axis of the fetus, the baby's brachial plexus would
undergo considerable stretching.
This may be compared to what happens when a tractor-trailer
truck approaches a low overpass
at high speed. While the tractor may pass under the bridge,
the trailer -- taller than the
tractor -- will ram into the overpass with high impact. The
momentum of the tractor will
result in large forces acting to separate it from its attached
trailer. Sandmire suggests
that an equivalent force acts upon a baby's brachial plexus
during some shoulder dystocia
Forces in deliveries
Some investigators have
actually used mechanical testing devices in an attempt to
the pressure placed on the brachial plexus of an infant during
deliveries -- with conflicting results.
Allen (1991) reported his use of tactile force sensing devices
on the tips of gloves during
a series of vaginal deliveries to measure the forces placed on
a baby's head by an
obstetrician's hands. The deliveries that were observed were
categorized into three groups:
Routine, difficult, and those involving shoulder dystocias. He
found that twice as much
force was applied to a baby's head during shoulder dystocia
deliveries as compared with
Gonik, however, one of Allen's co-investigators, subsequently
published a mathematical model
estimating the forces acting on the fetal neck overlying the
roots of the brachial plexus.
His findings mitigate the significance his and Allen's
previous work. He showed that the
forces applied by the clinician to the fetal neck were only
1/4 to 1/9 of those that
resulted from uterine contractions and maternal pushing
themselves in the second stage of
Most brachial plexus injuries occur to a baby's right arm
(60%). This is because babies
most commonly "present" into the mother's pelvis in the left occiput anterior position
(LOA). The LOA position is when the back of the baby's
head -- the occiput -- points towards the
mother's left arm while the fetal face is oriented towards the
mother's right buttock. In
this fetal position the baby's right arm will be anterior -- and
thus more likely to get caught
under the mother's pubic bone.
But brachial plexus injuries have also been reported in the
posterior shoulder. It is
thought that in these cases the posterior shoulder gets caught
on and restrained by the
sacral promontory while the remainder of the baby is being
pushed forward by the mother's
expulsive efforts or by her uterine contractions. The
posterior brachial plexus would thus
be stretched, potentially injuring it.
There are multiple reports of brachial plexus injuries which
appear to have occurred
sufficiently prior to delivery so as to not be causally
related to it. The evidence for the
timing of such in utero injuries comes from
electromyelographic studies, the measurement of
electrical transmission in muscle fibers.
It takes approximately ten days for a muscle to show an injury
pattern on electromyography
after the nerve innervation to that muscle is damaged.
Therefore if muscle damage from a
brachial plexus injury is measured by electromyography
immediately after delivery, the
injury had to have occurred at least a week or more before the
delivery took place.
Koenigsberg's (1980) report of this phenomenon is the most
detailed. He describes two cases
of brachial plexus injury in which electromyelographic
evidence suggested an
intrauterine -- prior-to-birth -- origin. One 3,625 gram baby had a
classic right Erb palsy at
birth. But electromyelographic studies of this baby's deltoid,
biceps and brachial radialis
muscles shortly after birth revealed multiple fibrillations
and positive injury waves in
addition to a greatly reduced numbers of active muscle units.
on the opposite arm were normal.
A second baby, a 3,180 gram term infant delivered via Cesarean
section, was noted at birth
to have left upper arm muscle weakness, loss of movement in
the left hand, and Horner's
syndrome -- classic for severe brachial plexus injury. Electromyelographic studies showed
clear-cut evidence of muscle fiber damage in the left arm. All
studies on the right side
Based on the
electromyelographic evidence, Koenigsberg concluded that the
injuries to the
two babies had to have occurred prenatally rather than being
caused by any injury associated
with delivery. Such muscle injuries from brachial plexus
electromyelographically at birth have also been reported by
Philpot (1995), Jennett (1992),
Brachial plexus injuries
following Cesarean section
Reports of brachial plexus injury in the absence of shoulder dystocia are subject to the
criticism that perhaps shoulder dystocias were under-reported
or that "excess' traction
might have been placed on the baby's head during the course of
a routine delivery. But
reports of brachial plexus injury following Cesarean section
are less subject to criticism.
There are many such reports in the literature:
Ecker (1997): Two infants born by Cesarean section who
plexus injuries, one of a nondiabetic mother, the other of a
Hardy (1981): Two infants born in vertex position at Cesarean
section who sustained
brachial plexus injuries.
McFarland (1986): Four patients delivered by Cesarean section
who experienced brachial
Graham (1997): Reported an Erb
palsy from cesarean section.
Gilbert (1999): Evaluated
data on all brachial plexus injuries from California in the
years 1994 to 1995. Of the 1,094,298 babies born in those two
years there were 1,611 brachial plexus injuries reported
(0.15%). Of these, 60 were from Cesarean sections.
The phenomenon of brachial
plexus injury following cesarean delivery -- and thus not
to shoulder dystocia -- is real. As has been shown, there is
much evidence to suggest that
not all instances of brachial plexus injury are due to
shoulder dystocia deliveries or to
the actions of a physician during such deliveries. Thus the
automatic assignment of
responsibility to an obstetrician or midwife for a brachial
plexus injury whenever a
shoulder dystocia delivery occurs is inappropriate and not
supported by the literature.
shoulder dystocia drill is a practice run-through by a labor
and delivery unit of a mock
shoulder dystocia delivery. It has been suggested both as a
practice protocol and as a
teaching technique for all members of the obstetrical team.
Some authors have stated that
it is the obligation of every delivery unit and every
obstetrician to participate in routine
shoulder dystocia drills as part of obstetrical readiness.
There is an excellent video tape
produced by the American College of Obstetricians and
Gynecologists (ACOG) -- AVL 103 -- that
describes and visually demonstrates a model shoulder dystocia
Although practicing and
preparing for any emergency is always a good idea, it is not
whether a formalized drill performed at regular intervals is
necessary to provide good care.
What is necessary, however, is that obstetricians, obstetrical
nurses, and everyone
involved with deliveries know that any vaginal delivery can
suddenly turn into a shoulder
dystocia emergency and that they are aware of the steps
necessary to resolve this emergency
in an orderly, efficient manner.
Careful documentation of instances of shoulder dystocia and
their resolution is extremely
important for two reasons:
1) Obstetricians want to
learn as much as possible from instances of shoulder dystocia
order to develop the best techniques for dealing with them.
2) Shoulder dystocia is so often the initiating cause of
Acker (1991) described what
careful documentation of a shoulder dystocia delivery should
1) Exact times of events.
2) Description of the
3) Estimation of the traction
The note must be legible and
must be written or dictated shortly after the events so that
is a contemporaneous medical progress note. Acker also
recommends that the note have a
specific form. This would include comments on:
1) Delivery time both for
head and body (the nurse should record this).
2) Episiotomy description and timing.
3) Whether or not anesthesia was present when the shoulder dystocia was recognized and any
additional anesthesia given.
4) Nasopharyngeal suction.
5) Initial traction before shoulder dystocia
is recognized, documenting force and duration.
6) Maneuvers used, listing
them in the order employed.
7) The force used described
in comparative terms such as average, maximal, etc.
8) Duration of maneuvers --
have the nurses know to record this.
9) Personnel -- identify all
10) Estimated fetal weight
and the actual birth weight.
Experience has shown that the
best defense in a medical liability action, whether involving
shoulder dystocia or any other situation, is thoughtful,
articulate, timely documentation of
each decision made in the course of treatment.
A thorough review of the literature on shoulder dystocia reveals the following:
1. Up until this year there has been no way for obstetricians to determine with any degree of accuracy which babies would be macrosomic and which babies would experience shoulder dystocia at delivery.
2. Likewise, until this year the various strategies proposed to attempt to reduce the number of shoulder dystocia deliveries and brachial plexus injuries would have all resulted in:
a. Hundreds or thousands of cesarean sections to prevent a single case of permanent brachial plexus injury
b. The potential medical complications from such interventions
c. The economic costs of such interventions
3. Although there are various techniques for resolving shoulder dystocias when they occur, these will not totally eliminate the incidence of brachial plexus and other birth injuries.
4. Brachial plexus injuries are often caused by factors not related to delery.
5. New research by multiple investigators has confirmed a linkage between maternal size, fetal weight and shoulder dystocia. Based on this association, Dr. Hamilton in Montreal, has developed a shoulder dystocia risk prediction tool (the CALM Shoulder ScreenTM, patent pending) that is able to predict more than half of those women who will encounter this complication. This methodology promises to change the current consensus of obstetrical opinion about the predictability of shoulder dystocia and to change the way obstetricians seek to prevent its occurrence and the complications that arise from it.
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