Erb's palsy results from injury to the fifth and sixth cervical nerve roots and is commonly associated with shoulder dystocia. Although approximately 80 percent of Erb's palsies resolve in three to six months, the 1 to 5 percent of cases that persist one year after delivery are usually the focus of litigation. Because Erb's palsy may occur without shoulder dystocia, the risk factors are not defined. Gherman and associates evaluated cases of Erb's palsy occurring in the absence of shoulder dystocia to see if they differ from those occurring after shoulder dystocia.

During the two-year study period, 126 cases of shoulder dystocia were identified among 9,071 vaginal deliveries. Among vertex-presentation fetuses, 40 cases of Erb's palsy were found. Seventeen cases of Erb's palsy without shoulder dystocia were compared with 23 cases associated with shoulder dystocia. Among the fetuses with shoulder dystocia, the risk of Erb's palsy was 18.3 percent (of which 1.6 percent had permanent injury). The only variable that differed between the two study groups was an increased incidence of second-stage length greater than 15 minutes among those without antecedent shoulder dystocia.

Neonates with Erb's palsy not associated with shoulder dystocia displayed a trend toward smaller birth weights and were more likely to have clavicular fractures. The affected Erb's palsy was more likely to occur in the anterior delivered shoulder with an identified shoulder dystocia, compared with the posterior arm when there was no shoulder dystocia. Erb's palsies without shoulder dystocia took longer to resolve and were more likely to persist at one year of age. Six of the seven persistent injuries occurred in infants weighing less than 4,000 g (8 lb, 13 oz). Both permanent injuries occurred in term macrosomic fetuses. The first case was associated with a four-hour second stage.

Results of this study demonstrate that most “no-shoulder” Erb's palsies do not represent underreporting of shoulder dystocia, and that not all cases are related to excessive traction on the nerve roots. The most important study result was the significantly higher rate of persistence found among cases of Erb's palsy without shoulder dystocia. There were also two instances of transient facial nerve palsy associated with brachial plexus injury. These observations suggest that pressure of the fetal cheek and shoulder against the symphysis pubis produced the injuries, rather than traction on the fetal head; as many as 50 percent of brachial plexus injuries can result from unavoidable intrapartum or antepartum events.

The authors concluded that Erb's palsy occurring without shoulder dystocia is a distinct entity and demonstrated that permanent brachial plexus injuries may occur before actual delivery of the fetal head. Attempts to recognize the at-risk fetus may not be successful.