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 that 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 0.5%-1.5% of all deliveries. Given that there are roughly 3 million babies born vaginally each year in the United States, this delivery complication will be experienced by roughly 15,000-45,000 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 disability. 

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 are still multiple, important recurrent questions:  Is shoulder dystocia predictable?  Can it be prevented?  Is there anything that can be done when it does occur to deliver the baby without brachial plexus nerve damage?  If there is an injury, was it caused by mismanagement on the part of the clinician 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 constitute the second largest category of indemnity payments in obstetrics, exceeded only by birth asphyxia.  In their defense, physicians contend that shoulder dystocia is a totally unpredictable event and that even with perfect management brachial plexus injuries will occur.  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 to fairly adjudicate responsibility in medical liability cases in which a baby has been injured during a shoulder dystocia delivery. 

Imortant new document

A recent report by the American College of Obstetricians and Gynecologist (2014) entitled Neonatal Brachial Plexus Palsy, written by a panel of the leading experts on shoulder dystocia and brachial plexus palsy from across the country, has added much specific information and informed opinion to the discussion of shoulder dystocia and brachial plexus palsy. This document can be ordered at acog.org.

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 at resuscitation.

Perhaps the most famous case of brachial plexus injury 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. Most likely, William suffered a brachial plexus injury. 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 photographs.

Shoulder dystocia occurs when, after delivery of the fetal head, the baby's anterior shoulder gets stuck behind the mother's pubic bone—or, occasionally, the baby’s posterior shoulder impinges on the mother’s sacrum. 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 clinician 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 the birth attendant 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. For instance, if there was no true shoulder dystocia during a particular birth in which there is a brachial plexus injury, can the physician reasonably be blamed for having applied excessive traction?

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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. However sometimes a baby’s posterior shoulder can get caught on its slight projection into the pelvis. The side walls of the maternal pelvis, although very important in determining how smoothly the process of labor will go, usually do not contribute to shoulder dystocia.

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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 overlap and the head as a whole can "mould"—go from perfectly round to more pointed and narrower. 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 upon which the baby's anterior shoulder gets caught. If this happens, the shoulders cannot deliver and a shoulder dystocia results.

As previously mentioned, 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 only a slight protrusion, is far less likely to impede the descent of the baby's posterior shoulder than is the mother’s pubic bone to block passage of the baby’s anterior 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 fetal dimensions. Thus if the head 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—such as in an especially large baby or a baby of a mother with diabetes—the chances of a shoulder dystocia occurring are much increased. Since larger babies, whether of diabetic mothers or not, 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 diabetic.

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 occur 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 ring" — trapping the baby in the uterus.

The above applies only to vertex (headfirst) deliveries. Breech deliveries, where the fetal legs and buttocks emerge first from the vagina, can also result in injury to the brachial plexus, producing the sorts of injuries discussed above. However, since vaginal breech deliveries are known to produce a higher rate of neonatal morbidity and even mortality, most breech babies in the United States are now delivered by cesarean section.

The incidence of shoulder dystocia is generally reported to be between 0.3 % and 1.5% with scattered reports listing values both higher and lower. 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 measured. For instance:

The Bulletin on Shoulder Dystocia by the American College of Obstetricians and Gynecologists (ACOG) lists the rate of shoulder dystocia as 1.4% of vaginal births.

The rate of shoulder dystocia in Great Britain reported by the Royal College of Obstetricians and Gynecologists as 0.6%

The rate of shoulder dystocia as reported by various authors is as follows:

Nocon (1993) 1.4

Baskett (1995) 0.6%

McFarland (1996) 0.7%

Bofill (1997) 3.3%

Gherman (1998) 1.4%

Stallings (2001) 1.7%

Foad (2008) 1.51

Chauhan (2014) 1.4

Tsur, in a 2011 study from Israel involving 240,000 deliveries, found that shoulder dystocia complicated 0.2% of all deliveries. Interestingly, in this study the rate of shoulder dystocia was seen to have declined from 0.4% in 1988 to 0.13% in 2009. The author feels that this was most likely due to an increasing rate of cesarean deliveries for suspected macrosomia.

Overland (2014), in one of the largest reports on the subject, reviewed data from 1,914,544 vaginal deliveries. The reported rate of shoulder dystocia in that group was 0.68%.

Parantainen (2014) evaluated 42,964 deliveries in Finland. He reported an incidence of shoulder dystocia of 0.42%.

Hansen, in a 2014 review article evaluating 28 published studies on the incidence of shoulder dystocia involving more than 16 million births, found a composite rate of shoulder dystocia of 0.4%.

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 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 (Gonik, 1991).

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 in a population with a larger than average percentage of macrosomic neonates or of diabetic mothers will have a much higher reported incidence of shoulder dystocia than if the population were a general one containing a more representational sample of both small and large babies and the normal percentage of mothers with diabetes.

Several recent studies have shown a lower rate of shoulder dystocia than has been reported in the past. This is despite the fact that on average newborns are getting larger. For instance, the percentage of very large babies (>4000 gms) has gone up 300% between 1970 and 1988 (Johar, 1988). Moreover, the last several decades has seen 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 should have lead to an increase the incidence of shoulder dystocia.

The likely answer to this paradox is several fold:

1. Physicians are now more aware of estimated fetal weight than in years past and are quicker to confirm this with ultrasound

2. Physicians are more reluctant to allow mothers with suspected macrosomic fetuses to have trials of labor but rather are recommending cesarean section for delivery.

3. Diabetic mothers with suspected macrosomic fetuses are especially being steered towards cesarean section for delivery.

One Step, Two Steps: An Interesting Theory

Iffy, in a 2015 article, claims that there has been an increased rate of shoulder dystocia and brachial plexus injury over the past several decades. He speculates that this increase is due to the advocacy of active management of delivery as proposed in the 1976 edition of Williams Obstetrics, whose major authors were Pritchard and McDonnell. This technique, called by some the “one step” technique, recommends attempting to deliver the infant’s shoulder immediately after the birth of the head. Locatelli (2011) has also discussed this issue.

Iffy notes that in prior editions of the Williams textbook (1961), whose major authors were Eastman and Hillman, it was expected that the shoulders would emerge in the contraction following delivery of the head—the “two-step” technique. Iffy denigrates the obstetrical experience of the authors of the newer edition, Prichard and McDonnell, saying that their expertise lay in cardiology, preeclampsia and basic sciences “rather than extensive experience in hands-on obstetrics.” Iffy also goes on to claim that prior to 2005 British obstetricians never adopted the “one step” policy and therefore had lower rates of brachial plexus injury—but that since they, too, have moved to the “one-step” technique they have seen an increase rate of BPI. Iffy concludes from the above that:

The rise of shoulder dystocia incidents since the introduction of active management suggest that elective use of traction is a major predisposing factor for both arrest of the shoulders and the deriving fetal injuries.”

However there are several aspects of Iffy’s contentions that deserve further scrutiny.

First of all, has there really been an increase in shoulder dystocia and brachial plexus injury—or has it just been reported more often due to medical-legal issues and better record keeping?

Second, Iffy’s arguments do not take into account the increasing percentage of macrosomic babies, the pronounced increase in maternal obesity, and the increasing use of epidural anesthesia as potential reasons for any increases in shoulder dystocia and brachial plexus injuries that might in fact have occurred.

Third, Iffy nowhere provides data to show that there is more traction involved in the “one-step” technique than the “two-step” technique.

Finally, Iffy’s argument only holds if clinician traction is the main cause of brachial plexus injuries when shoulder dystocias do occur. As will be shown below, while this has often been contended, it has never been proven—and there is much evidence against this hypothesis.

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 as it 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% (Lewis, 1995; Usta, 2008; Overland, 2009). Kleitman (2016) reported that previous shoulder dystocia was found to be an independent risk factor for recurrent shoulder dystocia with an odds ratio of 6:1. 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 with fetal injury.

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 asphyxia.

Brachial plexus injury

Brachial plexus injury is the classic injury following shoulder dystocia. It was first described by Duchenne in 1872.

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.

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There are two major types of brachial plexus injury: Erb palsy and Klumpke palsy.

Erb palsy, the more commonly occurring form, involves injury to 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: "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 with the forearm extended. Some have described this as the "waiters tip" position.

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.

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Patients seen with upper lesions immediately after birth—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 in the hand, arm, and shoulder caused by brachial plexus injuries 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 nonaffected arm.

While a sense of the degree and type of injury can be estimated by physical exam and clinical observation of the baby’s movement limitations, the true extent of brachial plexus injuries and the specific pathophysiology involved can only be definitively determined during surgical exploration of the brachial plexus at the time of a reparative procedure.

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 (Allen 2005, Lerner 2008, Ouzounian 2012) has led investigators to question whether or not brachial plexus injuries might have other etiologies. Such etiologies might be the stretching of the brachial plexus that can occur by the forces of labor (uterine contractions and maternal pushing) and—less likely—intrauterine cerebrovascular accidents (strokes), overstretching of the brachial plexus from fetal movement during the pregnancy, or spontaneous mal-development of the brachial plexus.

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 Horner's Syndrome.

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The natural history of brachial plexus injury

Fortunately, most brachial plexus birth injuries are transient. The majority of such injuries resolve by three months, with a range of 2 weeks to 12 months. Only 4 to 15% result in some degree of permanent injury as reported by various authors in the list below:

Johnson (1979) 7.8%

Sandmire (1988) 11.8%

Nocon (1995) 4%

Eckert (1997) 5-22%

Graham (1997) 20%

Chauhan (2014) 8%

Average: ~10%

Even though shoulder dystocia occurs in only 0.5% to 1.5% of all deliveries, the fact that there are approximately 3 million vaginal deliveries a year in United States means that many hundreds of babies will experience permanent brachial plexus injury. A little math tells the story:

—If the rate of occurrence of shoulder dystocia is approximately 0.5 to 1.5%, 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 6,666-20,000 vaginal deliveries

This means that there will be approximately 150-450 babies born each year in the United States with permanent brachial plexus injuries. 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.  

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 improving 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 such surgery.

Other neonatal injuries following shoulder dystocia deliveries

Fractured clavicle

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 both the length between the shoulders and the diameter of the fetal chest and may allow the shoulders and chest to deliver. This "safety valve" effect may in fact help reduce the incidence of severe brachial plexus injuries.

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.

Fractured humerus

This occurs in approximately 4% of infants with shoulder dystocia deliveries. While they may occur spontaneously, they are often the result of maneuvers employed to resolve a shoulder dystocia such as delivery of the posterior arm (see below). Such injuries heal rapidly and by themselves rarely result in litigation.

Contusions

The force with which an infant's shoulder is compressed against the maternal pubic bone and the pressure of the deliverer's hands on a 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. In fact, such bruises are common even in routine deliveries not involving shoulder dystocia or fetal injury.

Fetal asphyxia

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) 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, a baby’s umbilical artery pH declines at a rate of 0.04 units per minute. This would mean that at the five-minute mark following delivery of the fetal head, a 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.

Leung, in a more recent study—2011—found the drop in pH to be 0.011 per minute of head-to-body delivery interval as opposed to Wood’s 0.04/min. Both Leung (2011) and Lerner (2011) have shown that the risk of asphyxia during management of a shoulder dystocia delivery becomes significant at the 4-5 minute mark.

Cerebral palsy and fetal death are rare but unfortunately not unheard of consequences of prolonged head-to-shoulder delivery intervals following shoulder dystocia deliveries.

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 lack of umbilical flow — decreased delivery of oxygen to the fetus — may occur.

Menticoglou (2016) has recently proposed a new explanation as to why resuscitation may fail in some neonates after shoulder dystocia deliveries: hypovolemic shock. He notes that not only oxygen is interrupted by compression of the umbilical cord during shoulder dystocias, but fluid and blood flow cease as well. The fetal heart can pump blood out through the thicker arterial walls of the umbilicus but the thinner venous walls may collapse, not allowing oxygenated blood to return to the fetus from the mother. If substantiated, this phenomenon may lead to a change in how babies are resuscitated after severe shoulder dystocias.

Some authors—for instance Westgate (2011)—feel that the differences in cord arterial pH seen among infants following shoulder dystocia deliveries more likely reflect the condition of a fetus in labor prior to the occurrence of a shoulder dystocia rather than the deterioration over time during the shoulder dystocia resolution process.

Maternal injuries

The mother, too, is at some risk when a shoulder dystocia occurs. The most common complications she may suffer are excessive blood loss and vaginal and vulvar lacerations.

Significant maternal 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 when a shoulder dystocia occurs, post-partum bladder atony occurs frequently. Fortunately, it is almost always transient. Occasionally the mother's symphyseal joint becomes 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 dystocia.

The answer to this question by the vast majority of experts in obstetrics is “No”. This is confirmed by:

The ACOG Bulletin 40 (2002, reaffirmed 2015) which says “Shoulder dystocia is most often an unpredictable and unpreventable obstetric emergency.

The ACOG publication Neonatal Brachial Plexus Palsy (2014), p. 17: “Risk factors for shoulder dystocia are not reliable predictors for its occurrence.”

Williams Obstetrics (25th Edition, 2014): “Identification of individual instances [of shoulder dystocia] before the fact has proven to be impossible.…. Most cases of shoulder dystocia cannot be accurately predicted or prevented.”

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 minority opinion. The vast majority of obstetricians, including those who have done the most work on shoulder dystocia and brachial plexus injuries, 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 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 points of view:

Sensitivity: Are the risk factors associated with shoulder dystocia able to accurately identify most babies who will experience a shoulder dystocia at birth?

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%-1.5%) and the low positive predictive value risk factors for it have severely impeded the ability of obstetricians to utilize such information to advantageously alter clinical care.

The medical literature confirms this overwhelmingly.

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."

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.

Lewis (1998) noted that only 25% of shoulder dystocia cases had at least one significant risk factor.

Gherman (2002), among current leaders in the study of shoulder dystocia, has said the following:

“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.”

The obstetrical literature contains many other articles which share this point of view.

The general consensus in obstetrics is that both the sensitivity and positive predictive value for predicting shoulder dystocia is far too low to justify obstetrical interventions in hopes of avoiding it.

However, the above dictum has been challenged, particularly for shoulder dystocia with brachial plexus injury. There has been work by Emily Hamilton et al in Montreal using statistical methods to estimate the risk of shoulder dystocia with brachial plexus injury. The assessment of risk is based on the size of both the baby and the mother. This work indicates that it is possible to identify a small subgroup with very elevated risk of shoulder dystocia with brachial plexus injury, where the tradeoff between potential prevention and unnecessary intervention matches or exceeds the results using the ACOG intervention criteria.

The original algorithm evaluated the following factors: previous vagina birth, mother’s height and weight, gestational age, and estimated fetal weight. In a 2006 paper, Dyachenko and Hamilton showed that their algorithm was able to detect 50.7% of the cases of shoulder dystocia with some brachial plexus injury along with a false positive rate of only 2.7%. In a second study published in 2012 (Daly, 2012), the clinicians employed a similar algorithm prospectively, in just under 9000 deliveries from two New Jersey hospitals. Use of the algorithm resulted in a lowering of the rate of shoulder dystocia by 56.8% while not at all increasing the rate of primary cesarean sections.

Whether or not the Hamilton algorithm will change the current consensus in obstetrics that shoulder dystocia is unpredictable awaits further verification.

Categories of risk factors

The risk factors for shoulder dystocia can generally be divided into three categories:

Preconceptual — before pregnancy

Antepartum — during pregnancy

Intrapartum — during labor and delivery

A. Preconceptual risk factors for shoulder dystocia

1. Previous shoulder dystocia

Having had a shoulder dystocia in a previous delivery proves to be the most accurate predictor for recurrence of a 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 previous babies.

The risk of a woman having a repeat shoulder dystocia once having had one, as reported by various authors, is:

Smith (1994) 12%

Ginsburg (2001) 11%.

Gherman (2002) 11.9%

Mehta (2007) 10%

This compares with the baseline risk for shoulder dystocia of 0.5%-1.5%. Because of this significant increase in risk -- approximately 10-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 (1962) showed that shoulder dystocias occurred twice as often in obese women as 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.

Similar findings have been published by Hope (1998), Robinson (2003), and Kim (2014).

These reports, of course, beg the question as to whether or not obesity itself is risk factor for shoulder dystocia or whether it just reflects the fact that obese women are more likely to have macrosomic babies. Robinson (2003) studied this issue and found that maternal obesity was not significant as an independent risk factor for shoulder dystocia after adjusting for confounding variables. He found, as have others, that fetal macrosomia was the single most powerful predictor. Mehta (2014) also addressed this issue. He performed a multivariate logistic regression on the role of maternal obesity in shoulder dystocia and found, as had Robinson, that after considering other variables, obesity was not an independent risk factor for shoulder dystocia

Moreover, the literature has not shown the utility of using maternal weight to try to predict those women who will experience a shoulder dystocia at delivery. For instance, Hernandez (1990) showed that even in women weighing over 250 lbs., the rate of shoulder dystocia was no more than 5%. Thus any intervention that would have been undertaken based solely on maternal weight would have been without justification in 19 of 20 patients in his series.

There is a caveat, however. Given that more pregnant women than ever are obese, and that obesity has a marked correlation with fetal macrosomia — a known major risk factor for shoulder dystocia — it is likely that the continuing rise in the rate of maternal obesity will result in an increase in the occurrence of shoulder dystocia over the next decade.

3. Maternal age

Some studies have claimed that maternal age is a risk factor for shoulder dystocia. In one report from 2015, Zuarez-Easton reported that maternal age greater than 35 years has a 2.7 odds ratio for obstetrical brachial plexus injury.

But careful analysis reveals that maternal age is a risk factor for shoulder dystocia only in so far as maternal obesity, diabetes, excessive maternal 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 age and shoulder dystocia in isolation, Bahar (1996) did not find any difference in shoulder dystocia based on maternal age alone.

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 in obstetrics-- x-ray or other measurements of pelvic dimensions – was, for the most part, discarded years ago, for several reasons:

1. Except in the most extreme cases of congenital or pathological pelvic deformity, there is poor correlation between pelvic size and a woman's capacity to delivery vaginally.

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.

5. Multiparity

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. Overland (2012) confirmed these findings. Acker felt that this correlation between precipitous deliveries and shoulder dystocia was due to the fetus’s shoulders—in precipitous deliveries—not having time to align themselves in the oblique as opposed to the A-P orientation, thus predisposing them to shoulder dystocia.

Additionally, 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.

6. Gestational age

Paradoxically, Overland in a 2013 study showed that, after adjustment for birth weight, there is a consistent reduction in the risk of shoulder dystocia with increasing length of pregnancy. That is, per pound of baby the risk of shoulder dystocia was higher at 36 weeks than 40 weeks and higher at 40 weeks than 41 weeks. This trend was particularly pronounced in pregnancies complicated by maternal diabetes.

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 -- but in reality these are only markers for the increase of other primary risk factors

• There is no evidence linking the "abnormal pelvis" to shoulder dystocia

B. Antepartum factors risk factors for shoulder dystocia

1. Macrosomia

Other than a history of a previous shoulder dystocia, macrosomia is far and away the most significant risk factor for this condition. 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 conducted.

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:

More than 70% of all shoulder dystocias in his study occurred in infants weighing more than 4000 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 was 0.2%.

Nisbet (1998) published a chart showing similar data:

Sandmire (1998) likewise showed that the incidence of shoulder dystocia significantly increased with birth weight:

Vidarsdottir (2011) studied 41,000 deliveries in Iceland where babies generally tend to be large. Of the 41,000 neonates in his study, 343 were “extremely macrosomic (>5000 gms). This represented 0.9% of all deliveries. The odds ratio for shoulder dystocia in this group was 26.9. There were 46 shoulder dystocias among the 343 extremely large babies (14%).

Tsur (2012) evaluated 240,000 deliveries in Israel and determined that the odds ratio for shoulder dystocia in patients with macrosomia (defined as 4 kg) compared to babies weighing less than 4000gm was 16.1.

Revicky (2012) in England evaluated 9767 vaginally deliveries at 37 weeks or more between 2005 and 2007. The incidence of shoulder dystocia was 2.4%. The only independent risk factors for shoulder dystocia in his review were birthweight and instrumental delivery.

Cheng (2013) reviewed the medical records of 80,953 singleton deliveries at Prince of Wales Hospital in Hong Kong between 1995 and 2009. The incidence of macrosomia was 3.4%. The overall incidence of shoulder dystocia was 0.3%. The incidence rose with increasing birth weight. The odds ratio for shoulder dystocia with a birth weight of 4000 to 4199 g was 22.4 while the odds ratio for birth weight of 4200 g or more was 76.1.

Overland (2014) looked at this issue in a huge series of 1,914,544 deliveries. He found that 75% of all cases of shoulder dystocia occurred in deliveries of offspring weighing 4000 g or more. The association was slightly stronger in parous women than in primigravidas.

Parantainen (2014) evaluated 42,964 deliveries in Finland and reported that a baby with a birth weight of over 4000 g has a relative risk of 12.1 for shoulder dystocia compared to a population of lesser sized babies.

Temerinac (2014) found that in the weight interval 2500 – 4000, the rate of shoulder dystocia was 1.4% but that in babies bigger than 4500gm the rate was 16.2%.

Mehta (2014) showed that the incidence of shoulder dystocia increases with each 500 g of birth weight, reaching a tenfold increase by 4500 g.

Callaghan (2014) found adjusted odds ratios for shoulder dystocia of 15, 52, and 157 for birth weights of 4 – 4.5 kg, 4.5 – 5 kg, and greater than 5 kg respectively.

Hehir (2015) published a paper in which he showed that 17 of 120 infants with a birth weight of greater than 5000 g had a shoulder dystocia for a rate of 14.2%. Three of these suffered an Erb palsy, all of which resolved.

Macrosomia also seems to increase the rate of injuries following shoulder dystocia:

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 noninjured deliveries was 3160 g,

Kolderup (1997), in a review of the delivery of 2924 macrosomic babies at UCSF, reported that macrosomic infants had a six fold increase in significant injury from shoulder dystocia deliveries compared with controls.

What is macrosomia?

The definition of macrosomia has varied both through the years and according to the author(s) writing about it. The various cutoff points used to define macrosomia have been 4000 g, 4250, 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.

ACOG, in the new 2016 Bulletin on Macrosomia (#173), defines macrosomia this way:

At this time, it seems reasonable to recognize a continuum of risk and to divide macrosomia into three categories:

Birth weight of 4,000–4,499 g with increased risk of labor abnormalities and newborn complications

Birth weight of 4,500–4,999 g with additional risk of maternal and newborn morbidity

Birth weight of 5,000 g or greater with additional risk of stillbirth and neonatal mortality

The 25th edition of the Williams Obstetrics textbook (2014), on the other hand, says:

We are of the view that the upper limit of fetal growth, above which growth can be deemed abnormal, is likely two standard deviations above the mean, representing perhaps 3% of births. At 40 weeks, such a threshold would correspond to approximately 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 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 shoulders and trunk is likely to increase relative to the head, increasing its chances of shoulder dystocia.

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 fetal weight?

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 with a series of four specific steps in order to determine fetal position, fetal presentation, and to 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 infant weight at delivery. Moreover, multiparous women are often as accurate in their estimates of fetal weight as are clinicians and ultrasonic examinations (Chauhan, 1992).

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 formulas for ultrasound estimation of fetal size based on measurement of various fetal parameters. Most of these involved some combination of measurements of the fetal head, 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 for larger babies:

From these data it appears that sonographic models are not significantly superior to clinical examination in detecting newborns with birth weights greater than or equal to 4000 g.

There are many studies that confirm the inability of any current diagnostic technique to determine fetal weight prior to delivery to a range any better than 10-15% above or below the true birth weight.

Benson (1987): The use of ultrasound formulas to predict macrosomia was correct in only 47% of infants; the positive predictive value was only 36-43 per cent.

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.

Jazayeri (1999): Using a formula based on ultrasound-measured abdominal circumference in an attempt to determine which babies would weigh over 4500gm, the positive predictive value was only 9%.

Rossi in 2013 summarized the literature between 2000 and 2012 on the topic of prenatal identification, management, and outcomes of macrosomic infants. He found that

1. Both clinical and sonographic examinations are poorly predictive of macrosomia.

2. Knowledge before delivery that a neonate might weigh more than 4000 g does not improve neonatal outcomes.

3. Ultrasound has poor sensitivity in the detection of macrosomia: Between 9.4% and 15.3% in detecting birth weights greater than 4000 g. and between 6.3% and 30.4% for detecting a birth weight greater than 4500 g.

Burkhardt (2014), in a study of 12,794 deliveries, found that the mean percentage error of weight estimation by ultrasound was 8.8% in babies that had shoulder dystocia and 4% in a control group.

Shoulder/chest/abdomen ratios

As discussed above, both post-term growth and maternal diabetes result in the fetal trunk growing larger than 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 emerge from the vagina easily. With shoulders and trunk bigger than the fetal head, however, it is more likely that they will get stuck.

Several investigators have sought to measure the differences in size between fetal shoulders, trunk, and head circumference 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 improved accuracy: a positive predictive value of 78% for predicting birth weights over 4200 g. with a negative predictive value of 100%.

Cohen (1996) found that an abdominal diameter minus biparietal diameter measurement of greater than or equal to 26 mm was highly discriminative in the detection of shoulder dystocia and correlated well with incidence and severity.

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 high specificity."

Melendez (2009) showed that fetal abdominal circumference measurements of greater than 35 cm can be used to identify more than 90% of macrosomic infants—but also demonstrated that this method had a low positive predictive value in detecting specific cases of shoulder dystocia.

Burkhardt (2014), in an evaluation of almost 13,000 deliveries, found that there was a significant difference in

--abdominal diameter

--abdominal circumference

--abdominal diameter minus biparietal diameter

--abdominal circumference minus head circumference

between shoulder dystocia and control deliveries. Unfortunately, the positive predictive value when applying the proposed cut off for abdominal diameter minus biparietal diameter of 26 mm was only 7.6%. Burkhardt thus concluded that these measurements are not applicable as screening tools for predicting shoulder dystocia.

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 twofold:

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 dystocia deliveries.

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 the 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.

Delpapa's 1991 study showed that, at his institution, more than half 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 macrosomia was wrong 50% of the time both in underestimating and overestimating fetal weight.

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%.

Gonen (2000) evaluated 17 babies with brachial plexus injuries from a population of 16,416 deliveries. Only three of these injured babies were macrosomic.

Hansen (2014), in a review of literature on this topic, found that 27% of babies who experienced shoulder dystocias weighed less than 4000 g.

Burkhardt (2014) studied 12,794 vaginal deliveries and found that the majority of shoulder dystocia --56%--occurred in non-macrosomic fetuses

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.

Similar unsuccessful attempts to accurately ascertain fetal birth weight during the antenatal or intrapartum period have been published by Boyd (1983), Levine (1992), Chauhan (1992), Sandmire (1993), and Sacks DA (2000)

As the above data confirms, the general consensus of obstetricians who have done research in the area of shoulder dystocia is that the occurrence of shoulder dystocia based on estimations of fetal weight cannot 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 be established.

Sandmire, in his 1993 article, concludes:

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 to predict which babies will be macrosomic.

click on image to view larger image

2. Diabetes

Next to macrosomia, the factor most closely associated with shoulder dystocia is maternal diabetes in pregnancy. The prevalence of diabetes in pregnant women is increasing due to an older pregnant population, a higher rate of obesity, and more thorough antenatal detection (Young 2013).

One of the first clear-cut demonstrations of this was Acker's 1985 paper showing the following:

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:

Sandmire (1988) found a relative risk for shoulder dystocia in the babies of diabetic mothers of 6.5 compared to nondiabetic mothers.

In Al-Najashi's 1989 study, 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%.

Tsur (2011), in a study from Israel, showed that the odds ratio for shoulder dystocia with diabetes was 1.8 compared to nondiabetic mothers.

Overland (2013), in a population of just under 2 million deliveries in Norway, reported that shoulder dystocia occurred in 0.73% percent of all deliveries but 3.95% of deliveries in which the mother had diabetes.

Mehta (2014): Diabetes increases the overall risk of shoulder dystocia by more than 70%. In his study, the incidence of macrosomia was 21% among diabetic mothers versus 7.6% among those who were nondiabetic. Gram for gram, the incidence of shoulder dystocia and injury is higher in diabetic mothers.

Hansen (2014) reported that in his patient population the ratio of shoulder dystocia of nondiabetic to diabetic mothers was 0.6%:1.9%, a 201% increase.

There are two main reasons for this correlation between diabetes and shoulder dystocia. In the first place, diabetes in pregnancy is strongly linked to macrosomia. The growth of babies of diabetic mothers represents not only their genetic potential for growth but also reflects the conversion to fat of the excess glucose substrates present in both mother and baby. Secondly, as previously mentioned, growth is not as evenly distributed between the head and trunk in the babies of diabetic mothers as it is in those of nondiabetic mothers. 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 hyperglycemia.

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 dystocia.

Elliott (1982) claimed that by evaluating the chest and biparietal diameters in infants of diabetic mothers weighing more than 4000 g, he could reduce the incidence of traumatic morbidity at delivery from 27% to 9%.

Tamura (1986) found that in diabetic women fetal abdominal circumference values greater than the 90th 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 greater than 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 contradict the conclusions listed above. In addition, the results of the above 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 study, 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 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 sufficiently accurate 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.

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 is that macrosomia is as difficult to predict in diabetic mothers as it is 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 correlation between maternal weight gain and birth weight between women giving birth to average for gestation or large for gestational age infants

Several other 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' 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 clinical predictor.

5. Post-dates

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% prior to 41 weeks were (risk ratio 4.2) 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.

Overton in 2013 looked at this question in greater detail. He found that without correcting for weight, the rate of shoulder dystocia at 36 weeks is 27% of that at 40 weeks. However, after correcting for birth weight, the relative risk of shoulder dystocia at 36 weeks — compared to 40 weeks — was 1.68. Thus after adjustment for birth weight his results showed that there was a consistent reduction in the risk of shoulder dystocia from 36 weeks onward. This finding was particularly pronounced in pregnancies complicated by maternal diabetes.

Summary of antepartum risk factors

• Macrosomia and maternal diabetes are the main risk factors for shoulder dystocia

• Predicting fetal weight is extremely unreliable

• Other factors — maternal weight gain, fetal sex, and post dates — are secondary risk factors. They are correlated with an increased risk for shoulder dystocia but are only relevant to the degree that they increase the risk of fetal macrosomia

• Since multiparity increases the number of precipitous labors it may be a slight primary risk factor for shoulder dystocia

C. 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:

Baskett (1995) similarly showed a tenfold increase of shoulder dystocia and a fivefold increase in brachial plexus injury (BPI) with mid-forceps deliveries

Benedetti (1978) 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 a prolonged second stage nor a 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.

Hansen in 2014 reviewed the literature on shoulder dystocia with assisted vaginal deliveries. He found a shoulder dystocia rate of 0.6% with spontaneous deliveries but a rate of 2.0% with operative vaginally deliveries, a relative difference of 254%.

Parantainen (2014), in a Finnish study of 42,964 deliveries with 152 shoulder dystocias, found a relative risk of 3.98 between spontaneous deliveries and vacuum assisted deliveries.

Mehta (2014) found that shoulder dystocias increased by 35 to 45% in vacuum and forceps-assisted deliveries. For nondiabetic mothers with assisted deliveries this translated to shoulder dystocia rates of 8.6% for infants weighing 4000 to 4250 g, 12.9% for infants weighing 4250 to 4500 g, 23% 4500 to 4750 g, and 29% for infants 4750 to 5000 g. The total adjusted odds ratio for shoulder dystocia with instrumentally assisted deliveries was 1.9.

Zuarez-Easton (2015) reached a similar conclusion; he found an OR of 3.6 between spontaneous and vacuum assisted deliveries in which there was a brachial plexus injury.

Is there a difference between the use of forceps or vacuum when it comes to increasing the risk of shoulder dystocia?

Bofill (1997) found that there was a non-significantly higher incidence of shoulder dystocia with vacuum assist versus forceps: 4.6% versus 1.9%.

Dall’Asta (2016), on the other hand, showed no difference in the rate of shoulder dystocia between the use of vacuum and forceps. He postulated that the use of the vacuum or forceps to expedite fetal head delivery may interfere with the spontaneous mechanism of rotation of the trunk and ultimately with the descent of the shoulders in the birth canal. The lack of difference in his study between forceps and vacuum, as compared to Bofill’s study, may perhaps be attributed to the implementation of safer vacuum equipment since 1997.

Thus it is clear that deliveries requiring instrumental assistance have a higher risk of shoulder dystocia and brachial plexus injury than do spontaneous vaginal deliveries. 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, an altered distribution of fat between the fetal head, chest, shoulders, and abdomen, or descent of the shoulders in the A-P as opposed to an oblique orientation-- 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.

Acker in 1988 looked at the experience of the deliverer in relation to neonatal injuries following shoulder dystocia deliveries. He found that the number of Erb palsies following shoulder dystocias 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 stated,

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.

Hopewood (1982) found that there was a deceleration phase of active labor between 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.

Gross (1987) showed that a prolonged deceleration phase and long second stage contributed to brachial plexus injury risk but that these were only weak predictors.

Al-Natasha (1989) found that both a delay in the second stage of labor and slowed descent of the fetal head in obese multiparous women greatly increased the possibility that a shoulder dystocia would occur.

Weizsaecker (2007) found that brachial plexus injury is often but not always preceded by dysfunctional labor. In his study, active phase abnormalities predominated among the mothers who experienced a shoulder dystocia. The most important risk factor for shoulder dystocia was a long deceleration phase. This increased the adjusted odds of brachial plexus injury almost 6 fold.

Tsur (2011) showed that the odds ratio for shoulder dystocia with slow rate of descent during the second stage of labor was 2.4.

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.

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.

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.

Lurie (1995) found no correlation between the 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.

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 neonatal weight categories in relationship to shoulder dystocia deliveries.

To further complicate the issue, it is well known—as discussed above--that shoulder dystocias and brachial plexus injuries are often seen with short second stages of labor:

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.

Gonen (2000) reported that 7 of 17 patients (41%) with brachial plexus injury had second stages of labor shorter than 10 minutes

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 has to be 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 fetal weight.

Likewise with anesthesia; there is no reported increase in shoulder dystocia deliveries in labors in which conduction anesthesia is employed.

5. Episiotomy

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 obstetrical literature.

Gurewitsch (2004) demonstrated that management of severe shoulder dystocia with an episiotomy versus fetal manipulation alone or both does not influence neonatal depression rates.

Paris (2011) reviewed a total of 94,842 births in which there were 953 shoulder dystocias and 102 brachial plexus injuries. The rate of episiotomy with shoulder dystocia dropped from 40% in 1999 to 4% in 2009 with no change in the rate of brachial plexus injury per 1000 vaginally births.

Sagi-Dain in a 2015 review of 14 articles on the subject found no evidence supporting the use of episiotomy in the prevention and management of shoulder dystocia.

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 of the vagina and vulva 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 reach inside the vagina in order to perform rotational maneuvers or to attempt 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 unnecessary.

Thus the almost universal recommendation that an episiotomy be made during all shoulder dystocia deliveries is without literature or data support.

Combination of risk factors

As would be expected, several studies have shown that a combination of risk factors significantly increases the risk of shoulder dystocia.

Benedetti in 1978 published an article noting that the combination of macrosomia greater than 4000 g, prolonged second stage of labor, and mid pelvic operative vaginally delivery led to a 21% incidence of shoulder dystocia and a high rate of neonatal injury.

Mehta (2014) noted that in the setting of fetal macrosomia and a second stage of labor greater than two hours, performance of assisted vaginally delivery led to an increase rate of shoulder dystocia.

Busoni found that the combination of birth weight greater than 4000 g and vacuum delivery led to an odds ratio of 13.7 for shoulder dystocia; for birth weight over 4500 g with use of the vacuum the odds ratio was 21.5.

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 an obese mother with diabetes, an estimated large-for-gestational-age fetus, a prolonged second stage of labor, and a forceps delivery. The rate of shoulder dystocia in such a situation would approach 40%.

The preponderance of 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 managed when it does occur? Can it be resolved successfully without injuring the baby or the mother?"

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 are performed, and how effective they have proven to be.

Recognition

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 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 has emerged 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.

Turtle Sign

photo by Kristina Kruzan, kristinakruzan@gmail.com

Traction: "Excessive" or "Necessary" Force?

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 is 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. It is of interest that plaintiff lawyers in shoulder dystocia medical-legal cases and the expert witnesses they hire often say that there should be no downward traction utilized in resolving a shoulder dystocia delivery. Yet as the 2014 ACOG treatise on neonatal brachial plexus palsy states,

Because the position of the infant within the maternal pelvis will be at some angle relative to the horizontal plane (e.g., delivery table) during the final cardinal movements of labor, axial traction is generally applied in the direction or vector below the horizontal plane (also referred to as downward axial traction as distinguished from downward lateral traction or lateral bending).

It is also often said in court rooms that traction should never be applied to the fetal head during attempts to resolve a shoulder dystocia. This is certainly not the case. Unless a baby falls out of a mother—which is certainly not what happens with a shoulder dystocia—some traction—“gentle”, “moderate”—is always applied by the delivering clinician to the infant’s head. This is, in fact, the standard of care practiced by obstetricians across the United States and is the procedure describe in multiple obstetrical textbooks (see, for instance the Williams Obstetrics textbook or the Stanford Handbook of Obstetrics. Such assisting of delivery of the head is a necessary and approved obstetrical practice.

Normal Delivery Traction

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, 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 force 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, hypoxic neurologic damage, 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—and trained for--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 will occur.

What to do when a shoulder dystocia occurs

Several things should be done as soon as a shoulder dystocia is recognized. First, the obstetrician should announce that a shoulder dystocia is present. He or she should then request that a second obstetrician called, if possible, 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 also be called so as to be available to evaluate and potentially resuscitate the baby after delivery. Anesthesia staff should be summoned. If sufficient staff is available, one person should be designated as a note taker to record the timing of events.

How much time does one have to resolve a shoulder dystocia before hypoxic brain injury becomes a significant risk?

In general, the operator has up to five minutes to deliver a previously well-oxygenated term infant before an increased risk of asphyxial injury occurs.

Several studies over the years have attempted to determine the drop in fetal pH in the minutes following the onset of a shoulder dystocia. As noted previously, Wood (1973) was the first to examine this question in detail. He determined that for each minute during the interval between delivery of the fetal head and trunk in a shoulder dystocia delivery a fetus’s pH drops 0.04 units per minute. Subsequent studies have challenged this data; Leung in 2011 found the rate of pH drop per minute during a shoulder dystocia to be 0.01 unit. Yet as Gherman has shown (2006), there is not a good correlation between the head-to-body delivery interval and pH, pCO2, and pO2.

More recently, both Leung (2011) and Lerner (2011) have shown that the delivering clinician has roughly 4-5 minutes to resolve a shoulder dystocia before the risk of ischemic neuropathy becomes significant. This time frame of course depends upon the oxygenation and acidosis status of the fetus prior to the onset of the shoulder dystocia.

The Maneuvers

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.

(For an excellent in-depth review of shoulder dystocia resolution maneuvers and the traction forces involves, see Stitely and Gherman [2014].)

McRoberts maneuver and suprapubic pressure

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.

click on 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 frequently 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. Suprapubic pressure in conjunction with McRoberts maneuver is often all that is needed to resolve 50-60% of shoulder dystocias.

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 it does do, however, is to rotate the symphysis pubis toward the maternal head. This significantly changes 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.

Suprapubic Pressure

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 bottom 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. Whether or not an infant might be subject to injury with these maneuvers has been questioned by Gurewitsch and Allen (2005)--see below.

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 through the pelvis. Gurewitsch and Allen (2005) feel that these maneuvers place less stretch on a fetus’s brachial plexus than do the McRoberts maneuver or suprapubic pressure.

Delivery of the posterior arm

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 complete delivery of the remainder of the baby.

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.

Delivery of the posterior shoulder: Menticoglou and the posterior axillary sling

Menticoglou (2006) first described putting a finger into posterior axilla of the fetus to pull the posterior shoulder downward. This enables the grasping of the posterior arm, allowing it to be delivered, followed by delivery of the trunk. In 2009 Hofmeyr reported on a variation of this procedure. Instead of just using a finger, Hofmeyr recommends placing a soft plastic catheter sling around the posterior axilla and using that for traction.

Many, however, have voiced skepticism about these maneuvers. For if one has enough access to the fetal shoulder and axilla to place a finger or a sling around them, one wonders why the delivery could not have been performed as a routine rotational maneuver. Moreover, Cluver in 2015 reported on the use of the axillary sling in 19 cases. In five the baby had already died. Delivery was successful in 18 cases. There were 3 posterior humerus fractures, four cases of transient Erb palsy, and one case of permanent Erb palsy.

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.

Zavanelli maneuver

Although almost certainly performed by obstetricians and midwives in the past, this maneuver was first described in the obstetrical literature by 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. He was then able to perform an emergency cesarean section and deliver a live baby.

The first step in any cephalic replacement maneuver (now called the Zavanelli maneuver) is to set up for an emergency cesarean section. The fetal head is rotated to the occiput anterior position and flexed. Constant firm pressure is applied while pushing the head back into the vagina. Tocolytic agents such as terbutaline, nitroglycerin, 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 shoulder dystocia.

But a closer look at the data O’Leary reports is less than 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 a ruptured uterus and 5% suffered uterine lacerations.

Although Sanberg (1999) reported a much more optimistic experience with the Zavanelli maneuver -- 77.3% “success rate” involving 84 cases, neonatal complications in his series included clavicular fractures, humoral fractures, Erb palsies, quadriplegia, brain damage, mental retardation, various degrees of cerebral palsy and even mortality.

The data from these two series is sobering. While it is incumbent upon all obstetricians to know about the Zavanelli maneuver and to be able to perform it when other options for shoulder dystocia resolution have been exhausted, its significant potential for fetal and maternal injury must relegate it to the status of a "last ditch" procedure.

Transabdominal shoulder rotation (“Abdominal rescue”)

O’Shaughnessy in 1998 described another “last ditch” approach. He reported two cases in which, after unsuccessfully performing multiple shoulder dystocia resolution maneuvers, he performed a laparotomy and hysterotomy and then manually rotated the fetus’s stuck shoulders until he was able to complete a vaginal delivery.

Deliberate fracture of the clavicle

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 bone.

Symphysiotomy

Symphysiotomy is a procedure that had been performed in desperate situations in the past and is now performed only in areas remote from the ability to perform Cesarean sections on a rapid basis. 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 of a stuck fetus 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 enlarged pelvis.

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 joint separation.

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.

Following symphyseal 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 proving unsuccessful.

All-fours maneuver

In 1976, Ina May Gaskin, a midwife, 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 the dystocia 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.

Are any particular maneuvers better than the shoulder dystocia resolution maneuvers?

This is not at all clear. There have been multiple reports by different authors claiming various degrees of success with each of the shoulder dystocia resolution maneuvers.

Leung in 2011 evaluated delivery methods in 205 cases of shoulder dystocia. He found that following the failure of McRoberts maneuver the subsequent application of rotational methods or of posterior arm delivery has similarly high rates of success although the former may be associated with less fetal injury. The rate of either brachial plexus injury or humoral fracture with rotational methods was 4.4% vs. 21% with delivery of the posterior arm. Leung et al suggest that delivery of the posterior arm is less safe than rotational methods.

Also, Leung’s success rate with McRobert’s maneuver alone in his largely Chinese patient population was only 25% as compared to multiple American studies showing the success rate with this maneuver to be in the 40% range.

On the other hand, Hoffman (2011) reviewed 132,098 deliveries in which there were 2018 shoulder dystocias for a rate of 1.5%. One hundred one of these--5.2%--resulted in a neonatal injury. Delivery of the posterior shoulder was associated with the highest rate of successful delivery compared to all other maneuvers with no difference in the rates of damage to the newborn. Hoffman recommends that the clinician move to delivery of the posterior shoulder if McRoberts maneuver and suprapubic pressure prove unsuccessful in the management of shoulder dystocia. The need for additional maneuvers was associated with higher rates of neonatal injury.

Finally, Spain (2015), in a study of 231 women who experienced a shoulder dystocia, found that individual maneuvers were not associated with composite morbidity, neonatal injury, or neonatal depression after adjusting for parity and duration of shoulder dystocia. His conclusion:

There was no association between shoulder dystocia maneuvers and neonatal morbidity after adjusting for duration, a surrogate for severity. Our results demonstrate that the clinician should utilize the maneuver most likely to result in successful delivery.

So what can be said about the efficacy of the various shoulder dystocia resolution maneuvers?

1. The various maneuvers have not been subjected to a randomized trial

2. No maneuver has been clearly shown to be superior to any other in terms of successfully resolving a shoulder dystocia or reducing the rate of newborn injury.

What are some of the recommended protocols for resolving shoulder dystocia?

Many authors have proposed various protocols of prescribed maneuvers for the resolution of shoulder dystocia. Most are similar with only minor variations.

When a shoulder dystocia is recognized, it is generally agreed that 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 or Rubins 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 (2002, reaffirmed 2015), proposed the following sequence of maneuvers for reducing a shoulder dystocia:

1) McRobert’s maneuver and suprapubic pressure

2) Episiotomy—controversial

3) Rotational maneuvers

4) Delivery of posterior arm

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 posterior arm.

Gherman (1998) discussed the protocol for managing shoulder dystocia utilized at that time at the University of Southern California:

McRoberts maneuver

Suprapubic pressure

Procto-episiotomy

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.

Sentilhes (2016) discussed the guidelines for shoulder dystocia resolution from the French College of Gynecologists and Obstetricians (CNGOF)

Ask for help.

Perform McRoberts maneuver with or without suprapubic pressure.

Apply traction along the umbilical-coccygeal axis

Do either reverse Woods corkscrew maneuver or deliver posterior arm

Perform an episiotomy if one has not yet been performed one

Repeat maneuvers

Go to third line maneuvers.

Sentilhes adds two notes:

1. The available data do not allow us to conclude that any one of these maneuvers is superior to any other.

2. The performance of these obstetrical maneuvers for treating shoulder dystocia does not routinely require an episiotomy.

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 already in mind when a shoulder dystocia is encountered. The general consensus is that the best results in resolving shoulder dystocias are obtained when an obstetrician:

(1) Recognizes the shoulder dystocia

(2) Knows the different maneuvers involved in attempting to resolve shoulder dystocia

(3) Implements them in a carefully controlled, calm, and organized fashion.

Copyright © 2017 Henry Lerner