Shoulder Dystocia





Can shoulder dystocia and brachial plexus injury be prevented?

Up until this point we have been looking for various ways of predicting which babies and which labors will experience shoulder dystocia and possible brachial plexus injury. But such predictions, even if they can be made, are useless if there is no way to alter labor and delivery management so as to prevent shoulder dystocia and brachial plexus injury from occurring. Thus a most important question is this: Given what we know about shoulder dystocia and brachial plexus injury, is there anyway to prevent them?

As with the question of the predictability of shoulder dystocia, the answer to the question as to whether or not shoulder dystocia can be prevented has changed with the work of Gudmundsoon (2005) and Mazouni (2006) linking maternal size and fetal weight with shoulder dystocia and with the development of Hamiltonís shoulder dystocia risk predictive tool. Certainly if 50% or more of shoulder dystocias can be accurately predicted with a low false positive rate (2.7%), then prophylactic cesarean section for those patients thus identified becomes a reasonable preventive strategy. As further experience with the shoulder dystocia screening tool accumulates, this may well become the standard of care for attempting to prevent shoulder dystocia.

Up until this 2006, however, this tool had not been available. Let us look, therefore, at what information obstetricians have had up till now concerning the preventability of shoulder dystocia.

From the options available to obstetricians for intervening in pregnancy, labor and delivery, the only possible means for preventing shoulder dystocia would be:

  • To perform elective cesarean sections for suspected macrosomia
  • To induce labor in pregnant patients before their due dates in hopes of preventing babies from becoming macrosomic
  • To attempt through diet or blood sugar control to limit maternal weight gain

There are some authors who have always felt that shoulder dystocia could be prevented. O'Leary, in his book on shoulder dystocia, states:

A well-prepared obstetrician or midwife can anticipate this problem [shoulder dystocia] as a result of routinely identifying those risk factors that predispose to shoulder dystocia. Thus prevention requires identification of risk factors, which leads to anticipation of the problem . . . Identification of critical risk factors will lead to anticipation, which in turn will lead to prevention.

O'Leary then boldly goes on to say:

The presence of macrosomia of 4500 g alone is justification for cesarean section in nonobese women. The presence of macrosomia of 4000-4500 g may in itself be sufficient to warrant abdominal delivery when other risk factors, especially a platypoid (flat) pelvis, diabetes and/or obesity, are present.

But despite the certitude of his statements, O'Leary presents no data to support his recommendations.

Other authors have also tried to articulate guidelines for avoiding shoulder dystocia. Anchor (1988) has said:

We advocate the abdominal mode delivery for infants of diabetic gravidas whose best estimated fetal weight exceeds 4000 g.

Langer (1991) stated that if all infants of diabetic mothers who weighed 4250 g or more were delivered by cesarean section, the overall cesarean section rate would increase by only 0.26% while shoulder dystocia would be reduced by 76%. He goes on to acknowledge, however, that in the nondiabetic group there is no weight that provides an optimal threshold for cesarean section to avoid shoulder dystocia.

But statements such as these have represented the far fringe of obstetrical opinion. It has been the consensus of the vast majority of obstetricians who have studied the subject that there was no real way to figure out which babies are likely enough to have shoulder dystocia to warrant changes in the management of their labors. The basic issue is this: One can suspect shoulder dystocia all one wants. But is there some combination of factors that predicts shoulder dystocia with an accuracy great enough to make doing cesarean sections, performing early inductions, or making other changes in management a reasonable course of action? The answer up until now has been "No." Below is listed evidence that has supported this conclusion:

Basket (1995) : The profile of risk for shoulder dystocia -- prolonged pregnancy, prolonged second stage of labor, macrosomia, and assisted mid-pelvic delivery -- were not clinically useful because "the large majority of cases of shoulder dystocia occur in patients without these risk factors"

Resnick (1980): Most babies with shoulder dystocia do not have risk factors. "The diagnosis will often be made only after delivery of the fetal head."

Gherman (2002): "Most of these preconception and prenatal risk factors have extremely poor positive predictive values and therefore do not allow the obstetrician to accurately and reliably predict the occurrence of shoulder dystocia."

Lewis (1998): Only 25% of shoulder dystocia cases had at least 1 significant risk factor.

Acker's (1986) : Almost half (47.6%) of all shoulder dysoticas occurred in babies weighing less than 4000 g.

Cunningham, author of Williams Obstetrics, reports that 99.5% of babies weighing 4000-4500 gms had a safe vaginal delivery without shoulder dystocia.

Al-Najashi (1989) stated that 41% of shoulder dystocia deliveries occurred in infants of average birth weight, that is 2500 to 3999 g.

Eckert (1997): The greatest number of injuries occurred in nondiabetic patients with birth weights of less than 4000 g.

It is certainly clear that there are risk factors which do increase the odds of shoulder dystocia and brachial plexus injury occurring. But so many babies with each of these risk factors do not encounter shoulder dystocia and brachial plexus injury that it is difficult to justify changes in management of all labors on the basis of these suspicions.

Despite his statements in his 1992 book, even O'Leary, in a 1990 paper, acknowledges the unpredictability of shoulder dystocia: He lists multiple risk factors for shoulder dystocia -- and then goes on to prove that the majority of macrosomic babies do not have these factors!

The entire issue is best summed up in Practice Bulletin #40 "Shoulder Dystocia" (2002) by the American College of Obstetricians and Gynecologists. They find the preponderance of current evidence consistent with the following positions:

3. Most cases of shoulder dystocia cannot be predicted or prevented because there are no accurate methods to identify which fetuses will develop this complication.

4. Ultrasonic measurement to estimate macrosomia has limited accuracy

5. Planned cesarean section based on suspected macrosomia is not a reasonable strategy

6. Planned cesarean section may be reasonable for the nondiabetic with an estimated fetal weight exceeding 5000 g or the diabetic whose fetus is estimated over 4500 g

Up until this year, the vast bulk of the medical literature continued to support these contentions. However given the new work of Hamilton and her co-workers, these statements may have to be re-evaluated over the next several years.

Would elective cesarean section for suspected macrosomia be a reasonable strategy for decreasing the number of shoulder dystocias and brachial plexus injuries?

Many papers have been written trying to assess the utility of performing cesarean sections for suspected macrosomia in an attempt to reduce the risk of shoulder dystocia and permanent brachial plexus injury.

Gonen (2000) studied the use of physical examination and ultrasound during labor to identify babies suspected of being greater than 4500 g. His goal was to see if by performing cesarean sections in these cases he could reduce the rate of permanent brachial plexus injury. Macrosomia was suspected in 47 cases -- but was only confirmed at cesarean delivery in 21 of these (45% positive predictive value). Thus there were 26 unnecessary cesarean sections due to a false diagnosis of macrosomia. Moreover, over 84% of the macrosomic babies born from his subject population were missed. Of the 115 cases of macrosomia, only 21 were correctly identified in labor -- a dismal sensitivity rate of 18.3%. Of the 17 babies that developed brachial plexus injuries in his study, three were macrosomic -- but they were not identified prior to or during labor! The remaining 14 injured babies were not macrosomic. Thus, Gonen's attempt to decrease the brachial plexus injury rate by performing cesarean sections on suspected macrosomic babies missed most big babies and resulted in many unnecessary cesareans. He confirmed what is a major problem with any attempt to predict and prevent shoulder dystocia and brachial plexus injury: The group in which they occur most often is that of normal sized babies.

Many other studies have resulted in similar conclusions:

Rouse and Owen (1999) showed that prophylactic cesarean section would require more than 1000 cesarean sections and millions of dollars to avert a single permanent brachial plexus injury.

Basket (1995) stated that if in his series of patients all mid-forceps deliveries had been replaced by cesarean sections, 3268 cesarean section deliveries would have been performed to prevent 16 non-permanent brachial plexus injuries. Even if cesarean sections were performed only for babies suspected of being greater than 4500 g, 54 cesarean sections would have to be performed to prevent one case of non-permanent brachial plexus injury.

Eckert, in his 1997 paper, sums up the problem neatly:

In practice, only estimates of fetal weight, not actual weights, are available to practitioners seeking to predict the risk of birth injury. Weights estimated before delivery, whether by ultrasound or clinical estimation, are notoriously inaccurate. Even if we were able to identify a specific fetal weight that mandated cesarean section, any scheme that relied on estimated fetal weight to risk patients into cesarean delivery would result in the delivery of many infants appreciably smaller than the estimated fetal weight assigned them.

He points out that

The greatest number of injuries occurred in nondiabetic pregnancies with birth weights less than 4000 g. No protocol for managing macrosomia recommends cesarean delivery for estimated fetal weight of less than 4000 g.

In our opinion, the number of cesarean sections necessary to prevent a single birth injury in a normal glycemic population precludes our recommending mandatory cesarean delivery at any weight cutoff.

Delpapa (1991) studied nondiabetic women thought on ultrasound to have macrosomic fetuses. He concluded that he would have to do 76 cesarean sections to prevent five cases of shoulder dystocia:

Our study does not support the contention that elective cesarean section is justified in those women with fetuses suspected to be macrosomic as a means of preventing persistent infant mortality. A very large number of unnecessary cesarean sections would be performed without much preventive effect.

McFarland (1986) presented data by weight group showing how many cesarean sections would need to be performed to prevent even temporary brachial plexus injury:

Estimated wt

# C/S's
>4500 g 165
4000-4500 g 1383

His conclusion is that even if a reliable means of estimating fetal weight were possible, by performing cesarean sections for all babies estimated to be greater than 4500 g only 32% of all shoulder dystocias would be avoided. At any lower weight cut off, there would be far too many cesarean sections for far too little gain.

Rouse also tried to quantify the effectiveness of a policy of elective cesarean section for ultrasound-diagnosed fetal macrosomia. He found that in women without diabetes, if a cesarean section were performed for each baby with a suspected weight of greater than 4500 g, 3695 cesarean sections would have to be performed at an additional cost of $8.7 million for each permanent brachial plexus injury prevented.

Bryant (1998) data showed that even assuming ultrasound diagnosis to be accurate in predicting fetal weight, between 155 and 588 cesarean sections would have to be performed to obviate a single case of permanent injury, depending on the weight cut-off selected:

Our data show that a policy of elective cesarean delivery in cases of suspected fetal macrosomia had an insignificant effect on the incidence of brachial plexus injury. Although the contribution of this policy to the cesarean delivery rate was small, the number of cesarean deliveries required to prevent a single case of permanent  brachial injury was high and probably unjustified.

Gregory (1998) stated that if 5.5% of all brachial plexus injuries were permanent -- which his data demonstrated -- only one in 3833 macrosomic infants would have a persistent Erb palsy. Moreover, he found that one half of all of the shoulder dystocias in his series occurred in normal weight infants.

Kolderup (1997) found that a policy of elective cesarean section for macrosomia would necessitate 148 to 258 cesarean sections to prevent a single persistent injury. He feels that "these findings support a trial of labor and judicious operative vaginal delivery for macrosomia infants."

Sandmire (1993) discusses the difficulty in attempting to determine fetal size in utero:

Any approach using ultrasound would have to demonstrate that its use improves newborn or maternal outcome without disproportionate increases in morbidity and mortality. A barrier to achieving this goal is the inaccuracy associated with estimation of fetal weight. The current ultrasonic procedures for estimation of fetal weight are not accurate enough for detecting macrosomia defined by weight criteria.

And even if clinicians could determine fetal weight accurately, the frequency of persistent fetal injuries associated with vaginal birth of the macrosomic fetus is so low that induction of labor or cesarean birth is not justified on that basis. Delivery decisions based on inaccurate estimated fetal weights should be avoided.

He also composed a chart drawn from data in several other studies in which he evaluated the rate of permanent brachial plexus injuries and the number of cesarean sections that would be necessary to avoid them:

Study C/S to prevent BPI injuries C/S to prevent permanent BPI injury
Gordon (1973) 526 10,520
Sandmire (1988) (no data) 7403
McFarland (1986) 1922 39, 840
Modanlou (1980) 588 11,700

Sandmire (1996) concludes that a policy of employing cesarean section for suspected macrosomia in hopes of preventing permanent brachial plexus injury will not work because of:

1. The inaccuracy of ultrasound in estimating fetal weight

2. The increases in morbidity and mortality that would occur from the very large numbers of cesarean sections so generated.

3. The many cesarean sections would have to be done to prevent one significant fetal injury

Sandmire also takes care to distinguish minor injuries, such as clavicular fracture and transient brachial plexus injury, from severe persistent fetal injuries. He admonishes anyone considering the issue of cost vs. benefit in the management of suspected macrosomia to make decisions based only on significant fetal injuries, such as permanent brachial plexus injuries and severe neurologic damage.

Summarizing, the major conclusion of most of the obstetrical literature discussing the strategy of performing cesarean sections for suspected macrosomia is that it would not be practical because it would require far too many unnecessary interventions for the benefits that would be obtained.

Cesarean sections are not without risk, especially for diabetic and/or obese women

Although cesarean section is one of the most commonly performed operations in the United States, it still carries much greater risk than does a vaginal delivery. These risks include blood loss, infection, damage to other pelvic organs, and respiratory emergencies. Moreover, the recovery period is longer and more painful and performing one cesarean section greatly increases the likelihood that a woman will have her next baby by cesarean section as well. Finally, total hospital care for women delivering a baby via cesarean section is 50%-100% more expensive than the cost of a vaginal delivery.

Thus in order to justify the increased risk, pain, and expense of performing cesarean section in hopes of avoiding shoulder dystocia and permanent brachial plexus injury, there has to be substantial evidence that this is an effective policy. As has been shown, such evidence has up until now been lacking. In fact, the evidence has been contrary to this supposition.

What about early inductions as a means of avoiding shoulder dystocia and brachial plexus injury?

Many have thought that by cutting off one to two weeks of growth of a fetus at term, a baby might be delivered small enough to avoid shoulder dystocia and the risk of permanent brachial plexus injury. The problem with this theory is that there is no data to support it.

In the first place, the growth rate of babies differs significantly, both between babies and at various points in pregnancy for each baby. Thus it is impossible to estimate how much additional growth is prevented by "early delivery".

Most importantly, studies looking at this means of attempting to prevent shoulder dystocia have never been successful in reducing the number of macrosomic babies or showing that such a program reduces the risk of shoulder dystocia:

Del Papa (1991) found that early induction did not decrease infant morbidity.

Gonen (1997) randomized patients suspected of macrosomia based on ultrasound examination to an early induction group -- 134 patients -- or a routine pregnancy follow-up group -- 139 patients. There was no statistically significant difference in shoulder dystocia between the two groups.

Several authors -- Leaphart (1997), Friesen (1995), Combs (1993) -- have even shown that this approach of early induction actually increased the cesarean section rate with no decrease in the incidence of shoulder dystocia.

So, can shoulder dystocia be prevented?

A review of the literature indicates that the answer to this question has up until this year been "No." Estimates of fetal weight are unreliable. It is impossible to accurately tell which babies will be macrosomic. And it has previously been impossible to reliably determine which babies will develop shoulder dystocia. Based on previous information available to obstetricians, a policy of prophylactic cesarean section would have required huge numbers of operations to prevent a single case of permanent brachial plexus injury. It is also the case that a policy of elective induction has not been shown to decrease the number of shoulder dystocias.

Hope for the future

As has been discussed, there is now published research, based on sophisticated statistical and mathematical analysis of a large numbers of shoulder dystocia cases, that shows that it is possible to identify 50% or more of those mothers and fetuses at highest risk for shoulder dystocia.

Dr. Emily Hamilton and her team of researchers in Montreal have developed a formula considering maternal height, maternal weight, parity, gestational age, estimation of babyís weight, and maternal history of gestational diabetes or previous shoulder dystocia that, when tested against several large independent samples of patients who had experienced shoulder dystocia with permanent injury, consistently identified 50-70% of them with a false positive rate (rate of additional cesarean sections) of only 2.7%. (Dyachenko,Hamilton 2006 and subsequent unpublished data). This tool has been commercialized into a web-based application by LMS Medical Systems and labeled the CALM Shoulder ScreenTM (patent pending) -- see for more information.

As this probabilistic tool becomes more widely utilized, it may well be possible to prevent a significant proportion of brachial plexus injuries by recommending prophylactic cesarean section to those women identified as being at high risk for shoulder dystocia.

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Copyright © 2006 Henry Lerner

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