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

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

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

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

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

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

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:

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.

Hope for the future

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Copyright © 2006 Henry Lerner