Infants of insulin-dependent diabetic mothers are at risk for neonatal polycythemia, hyperbilirubinemia, respiratory distress syndrome (RDS), and hypoglycemia. The purpose of this study was to determine whether labor and delivery management of diabetes may influence the rate of these complications. We hypothesized a priori that: infants of diabetic mothers delivered by cesarean section have a lower rate of neonatal polycythemia and hyperbilirubinemia, but a higher rate of RDS, than infants of diabetic mothers delivered by vaginal route, and poor glycemic control during labor increases the rate of neonatal hypoglycemia. We therefore prospectively studied 122 pregnancies in 100 well-controlled insulin-dependent diabetic mothers. Intravenous glucose and/or insulin was infused during labor to maintain capillary glucose concentration between 70 and 100 mg/dl. Fifty-six pregnancies were concluded by primary or elective cesarean section (group 1), 36 by cesarean section following spontaneous or induced labor (group 2), and 30 by spontaneous or induced vaginal delivery (group 3). Hemoglobin A1, birthweight, and gestational age were similar in all three groups. The rate of neonatal polycythemia was significantly lower in the cesarean section subjects, groups 1 and 2, as compared to group 3 (P less than 0.04). The rate of neonatal hyperbilirubinemia was significantly lower in group 1 (P less than 0.05) as compared to groups 2 and 3. The rate of RDS was higher in group 1 (versus groups 2 or 3), but did not reach significance on initial analysis (P = 0.06); however, group 1 was associated with a significant risk for RDS when corrected for the confounding variables of gestational age and neonatal asphyxia as defined by Apgar scores.(ABSTRACT TRUNCATED AT 250 WORDS)