The author reports no financial relationships relevant to this article.
Brachial plexus injury is a dreaded sequela of shoulder dystocia, one that lies at the root of many medical liability disputes. Although brachial plexus injury cannot be prevented, most of the commonly used maneuvers for freeing a stuck shoulder are designed to maximize fetal safety and minimize injury.
What is the standard of care when dystocia occurs? Several respected sources have offered conflicting recommendations, particularly in regard to maternal pushing once dystocia is diagnosed. My aim in this article is to clarify the issue.
Endogenous force versus exogenous force
The introduction to the American College of Obstetricians and Gynecologists’ practice bulletin on shoulder dystocia, published in November 2002, provides a useful summary of much of our current knowledge:
Shoulder dystocia is most often an unpredictable and unpreventable obstetric emergency. Failure of the shoulders to deliver spontaneously places both the pregnant woman and fetus at risk for injury. Several maneuvers to release impacted shoulders have been developed, but the urgency of this event makes prospective studies impractical for comparing their effectiveness.1
Because prospective studies are unlikely ever to be performed, some investigators have turned to mathematical modeling to learn more about the forces exerted on the fetal neck overlying the roots of the brachial plexus when a shoulder is impacted against the symphysis pubis.
Gonik and colleagues2 performed elegant modeling of the pressure between the base of the fetal neck and symphysis pubis during dystocia. They utilized data on birth forces gathered by CaldeyroBarcia and Poseiro3 in their classic work on intrauterine pressure. Gonik and colleagues also used data from Allen and associates,4 who measured the force of clinician-applied traction after delivery of the head by having clinicians wear sensory gloves that recorded the force of traction applied.
Gonik and associates2 concluded that the pressure resulting from endogenous forces is four to nine times greater than the pressure generated by a clinician. “Neonatal brachial plexus injury is not a priori explained by iatrogenically induced excessive traction,” they wrote. “Spontaneous endogenous forces may contribute substantially to this type of neonatal trauma.”
How an understanding of endogenous forces alters management
Although fewer than 10% of cases of shoulder dystocia result in permanent brachial plexus injury,1 such injuries are a major source of malpractice litigation in obstetrics, as I noted at the beginning of this article. In most such cases, injury is blamed on excessive traction by the physician (FIGURE). Newer data, such as the study by Gonik and colleagues,2 may implicate expulsive force (ie, maternal pushing) as another, perhaps greater, cause.
As long ago as 1988, Acker and colleagues5 reported on their experience with Erb’s palsy, which was associated with rapid delivery and unusually forceful expulsive effort in one third of cases. Their findings suggest that, when shoulder dystocia occurs and additional maneuvers are necessary to deliver the impacted anterior shoulder, the contribution of potentially harmful endogenous forces should be kept in mind. Counterintuitive strategies, including having the mother stop pushing until the anterior shoulder is freed, may help limit injury.
FIGURE Maternal pushing may contribute to injury
When shoulder dystocia occurs, the progress of labor is interrupted and brachial plexus injury can result, a common cause of litigation. Until now, plaintiff’s attorneys have tended to blame these injuries on the obstetrician and “excess” traction, but it now appears that maternal pushing contributes as well—possibly, to a greater degree than any effort by the physician.
How confusion crept into the literature
The 21st (current) edition of Williams Obstetrics,6 in the section on management of shoulder dystocia, states that “an initial gentle attempt at traction assisted by maternal expulsive efforts is recommended.” There is no reference for this statement. However, a look at the 19th edition of the textbook7 reveals identical wording, and the reference cited is ACOG Technical Bulletin No. 152 (August 1991), entitled Operative Vaginal Delivery. A subsequent version of the same bulletin (no. 196 from August 1994) contains identical wording. By the time that version was replaced by ACOG Practice Bulletin No. 17 (June 2000), however, it no longer contained any information on shoulder dystocia. Instead, ACOG published Practice Pattern No. 7 (October 1997), entitled Shoulder Dystocia. This document did not recommend maternal expulsive force after a diagnosis of shoulder dystocia—in fact, maternal force was not even mentioned. Nor is it mentioned in the current practice bulletin (no. 40 from November 2002), which replaced the previous version of Shoulder Dystocia.