Limited usefulness of fetal weight in predicting neonatal brachial plexus injury

OBJECTIVE: The objectives were to determine the neonatal morbidity rate from vaginal birth and examine fetal weight-based injury-prevention strategies. STUDY DESIGN: Selected neonatal morbidities were categorized by birth weight for all vertex vaginal deliveries occurring during a 12-year period. Sensitivity, specificity, and predictive values for brachial palsy were calculated at increasing birth weight cutoff levels. A policy of cesarean delivery far macrosomic infants was evaluated. RESULTS: There were 80 cases of brachial palsy among 63,761 infants (0.13%). In mothers without diabetes, rates in the 4500- to 4999-g and >5000-g groups were 3.0% and 6.7%, respectively. A threshold of 3700 g had a sensitivity of 71% and a specificity of 86%; the positive predictive value was 0.56%. To prevent a single case of permanent injury, 155 to 588 cesarean deliveries are required at the currently recommended cutoff weight of 4500 g. CONCLUSIONS: The rates of lasting morbidity do not justify routine cesarean delivery for infants without diabetic complications weighing <5000 g.