Since shoulder dystocia is known to be associated with macrosomic fetuses and risk is increased in babies of diabetic mothers, various strategies have been proposed utilizing this knowledge to attempt to decrease the incidence of shoulder dystocia and hence related brachial plexus palsies. Let us examine some of these proposed strategies

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 true macrosomia in his series, 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:

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

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 shoulder dystocias would be avoided. At any lower weight cut off, there would be far too many cesarean sections for far too little gain.

Delpapa (1991) studied nondiabetic women thought via ultrasound to have macrosomic fetuses. He concluded that he would have to do 76 cesarean sections to prevent five cases of shoulder dystocia. If the rate of permanent brachial plexus injury is 1 in 100 shoulder dystocias, that would mean 7600 cesarean sections to prevent 1 permanent injury.

Sandmire’s 1993 article discussed in some detail the difficulty of 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 to mother and baby. A barrier to achieving this goal is the inaccuracy associated with estimation of fetal weight. According to Sandmire, ultrasonic procedures for estimation of fetal weight are not accurate enough for detecting macrosomia.

He goes on to say that 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 what are likely to be inaccurate estimated fetal weights should be avoided.

Sandmire also drew up 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:

Sandmire reiterated his thinking in another paper published in 1996. In it he 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 that 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 recommends that anyone considering the issue of cost vs. benefit in the management of suspected macrosomia should make decisions based only on significant fetal injuries, such as permanent brachial plexus injuries and severe neurologic damage.

Several other authors have concurred with Sandmire’s conclusions:

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, confirms the problems described by previous authors: In practice, only estimates of fetal weight, not actual weights, are available to clinicians 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.

Eckert points out that the greatest number of injuries occurred in nondiabetic pregnancies with birth weights less than 4000 g.—and no protocol for managing macrosomia recommends cesarean delivery for an estimated fetal weight of less than 4000 g. Eckert concludes:

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. 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.

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."

Bryant’s data (1998) 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.

Rouse and Owen (1999) quantified the effectiveness of a policy of elective cesarean section for ultrasound-diagnosed fetal macrosomia. They 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 for each permanent brachial plexus injury prevented.

Homer (2011) evaluated 591 extremely obese women in England between 2007 and 2008 He found no significant differences in anesthetic, postnatal, or neonatal complications between women with planned vaginally delivery and planned cesarean delivery with the exception of shoulder dystocia--3% versus 0%. None of the infants with shoulder dystocia suffered permanent brachial plexus injury. The study does not provide evidence to support a routine policy of cesarean delivery even for extremely obese women. The entrance criteria for the study was a BMI of equal to or greater than 50.

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. As noted, the new work by Hamilton’s group may over the next several years invalidate these conclusions.

Very importantly, there is one more issue that needs to be addressed in discussing the above question. It is that

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 for the mother than does a vaginal delivery. These risks include blood loss, infection, damage to other pelvic organs, and respiratory emergencies. Moreover, the recovery period following a cesarean section is longer and more painful than after a vaginal delivery, 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 a 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 is currently 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 born at a lighter weight than if delivered at term. This difference in newborn weight might be enough to avoid shoulder dystocia and the risk of permanent brachial plexus injury. Is this a viable policy?

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". Moreover studies testing this hypothesis—until very recently—have been disappointing.

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.

Sanchez-Ramos (2002) reviewed 11 studies with 3751 subjects, 2700 of whom were managed expectantly while 1051 underwent labor induction. Compared with those whose labor was induced, women who experienced spontaneous onset of labor had a lower incidence of cesarean section (RR 0.39) and higher rates of spontaneous vaginally delivery (RR 2.07). No differences were noted in the rates of operative vaginally delivery, incidence of shoulder dystocia, or abnormal Apgar scores. Sanchez-Ramos’s summary: labor induction for suspected fetal macrosomia results in an increase cesarean delivery rate without improving perinatal outcomes.

Thus until recently there was no data to support a policy of early induction in an attempt to decrease the rate of shoulder dystocia. More recent literature, however, seems to show that this such a policy might, in fact, have some benefit

Boulevain in 2015 compared induction of labor with expectant management for large for dates fetuses to try to prevent shoulder dystocia. His trial ran between 2002 and 2009 in centers in France, Switzerland, and Belgium. Women suspected of carrying a macrosomic fetus were divided into 2 groups, one in which women were induced between 37 and 38 6/7 weeks of gestation, the other receiving expectant management.

Boulevain’s findings contradicted those of all previous studies: In his series, induction of labor substantially reduced the risk of shoulder dystocia and associated morbidity compared with expectant management (RR 0.32). The rate of significant shoulder dystocia in the induction of labor group was 1% while in the expectant management group it was 4%. The risk ratio for “any” shoulder dystocia—as opposed to “significant” shoulder dystocia--was 4% compared with 8% for a risk ratio of 0.47. Moreover, the cesarean section rate in the induction group was 28% versus 32% for the expectant management group.

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Copyright © 2017 Henry Lerner