Relationship between parity and brachial plexus injuries.

Objective: 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.
Study Design: 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.
Result: 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).
Conclusion: 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.