Perinatal injury to the brachial plexus is uncommon, occurring in 0.05 to 0.26 percent of deliveries. Although the injury is transient in 70 to 95 percent of cases and full function of the upper limb is attained, the condition is often a source of litigation, as the etiology is assumed to be birth trauma. In more than one half of cases of brachial plexus dysfunction at birth, no shoulder dystocia or other complication of pregnancy or delivery can be documented; this finding has led to speculation that the cause of brachial plexus dysfunction may not necessarily be birth trauma. Gilbert and colleagues studied pregnancy and birth records from over 300 hospitals in California to examine risk factors and maternal-fetal complications associated with brachial plexus injury.

The authors studied records of over 1 million women who delivered during a two-year period. Brachial plexus injury was documented in 1,611 (0.15 percent) cases. The risk of brachial plexus injury was related to birth weight, mode of delivery, presentation and other factors such as diabetes. Approximately one half of cases were related to shoulder dystocia and about one quarter to other malpresentations. The odds ratio for shoulder dystocia was 76.1; for other malpresentations, it was 73.6. Compared with spontaneous vaginal delivery, the odds ratio increased with operative vaginal delivery from 2.7 for vacuum extraction to 3.4 for forceps. Cesarean delivery was protective (odds ratio: 0.2). The highest rates of brachial plexus injury (7.8 percent) occurred in macrosomic infants (those weighing more than 4,500 g [9 lb, 15 oz]) who were born to diabetic mothers by assisted vaginal delivery. Prematurity and fetal growth retardation were associated with reduced rates of brachial plexus injury. The condition was associated with complications of delivery such as asphyxia, subarachnoid and intraventricular hemorrhage, and prolonged neonatal hospital stay.

The authors conclude that brachial plexus injury is not inevitably linked to shoulder dystocia or birth trauma. The condition may result from abnormalities occurring during pregnancy or delivery. Even in women at highest risk, it is estimated that a policy of elective cesarean delivery would prevent only about 19 percent of cases and is not justifiable.

editor's note: Anything less than a perfect result of pregnancy is accompanied by a desire to find the reason for the unfortunate outcome. This sometimes results in complex legal proceedings seeking to apportion blame. As is the case with cerebral palsy, brachial plexus dysfunction is probably the “final common pathway” for a wide range of conditions that compromise the nervous system before or during birth. While the previous explanation of birth trauma as the inevitable cause of these conditions was understandable and uncomplicated, it resulted in a culture of blame, guilt and distrust that undermined the confidence of patients in their physicians. Every effort must be made to ensure safe, uncomplicated deliveries and appropriate allocation of responsibility when things go wrong. Not all bad outcomes can be attributed to medical care.—a.d.w.