The objective of the study was to examine the association between time of delivery and neonatal outcomes in term deliveries.

We conducted a retrospective cohort study of all term pregnancies delivered at an academic institution with 24-hour in-house obstetric and anesthesia coverage. Time of delivery was categorized as day (7 am to 6 pm), evening (6 pm to 12 midnight), and late night (12 midnight to 7 am). Outcomes included 5-minute Apgar less than 7, umbilical artery pH less than 7.0, base excess less than −12, admission to the neonatal intensive care unit (NICU), and neonatal death. We excluded patients delivered via cesarean delivery not in labor. We had greater than 80% power to detect a 25% difference in Apgar score, base excess, and admission to the NICU and 80% power to detect a 50% difference in umbilical artery pH less than 7.0.

Among the 34,424 deliveries meeting inclusion criteria, 15,664 were during the day, 8495 were during the evening, and 10,265 were during the night. In univariate comparisons, there were no statistically significant differences in neonatal outcomes. For example, the rate of pH less than 7.0 was 0.7% during the day, 1.0% in the evening, and 0.6% at night (P = .12). Admissions to the NICU were 3.6% during the day, 3.7% in the evening, and 3.5% at night (P = .81). When we controlled for obstetric history, demographic factors, and labor characteristics, there were still no differences in rates of either neonatal morbidity or mortality by time of delivery.

At our institution, we could not demonstrate any significant differences in neonatal morbidity or mortality by time of day among neonates delivered at term. These data can be used to counsel patients and families concerned about differences in time of delivery and potential impact on their infant's health. Future research should include time of delivery in relation to maternal and neonatal outcomes in various types of inpatient settings.