Relationship between parity and brachial plexus injuries.

Few characteristics have been identified as risk factors for brachial plexus injuries. We sought to investigate a potential relationship with multiparity based on clinical observation at our institution.In this retrospective case series, we analyzed all brachial plexus injuries recognized at or after delivery between October 2003 and March 2013 (n=78) at a single academic medical institution. Patient, infant, labor and delivery characteristics were compared for women with and without prior vaginal deliveries.Of the 78 injuries, 71 (91%) occurred after a vaginal delivery and 7 (9%) after a cesarean delivery. Of the 71 injuries after a vaginal delivery, 58% occurred in women with a prior vaginal delivery (n=41, 5.7 per 10 000 live births) compared with 42% without a prior vaginal delivery (n=30, 4.0 per 10 000 live births). Multiparous patients had shorter labor courses and fewer labor interventions than nulliparous patients. Providers clinically underestimated the birth weights to a greater extent in multiparas than in nulliparas (median underestimation 590 vs 139 g, P=0.0016). The median birth weight was 4060 g in the multiparous group, which was significantly larger than affected infants born to the nulliparous group (3591 g, P=0.006). The affected infants of the multiparous group were, as expected, significantly larger than their previously born siblings (median 567 g larger, P<0.001).Brachial plexus injuries occurred as frequently in multiparous patients as in nulliparous patients. In general, multiparous patients are more likely to have larger infants; however, providers significantly underestimate the birth weight of their infants. The findings of this study should deter providers from assuming that a prior vaginal delivery is protective against brachial plexus injuries.