To assess the independent association between overnight or “off-peak” hour delivery and 3 neonatal morbidities strongly associated with childhood neurocognitive impairment.

Retrospective population based cohort study of all infants with birth weights of 500-1499 g born without severe congenital anomalies in California or Pennsylvania between 2002 and 2009. Off-peak hour delivery was defined as birth between 12:00 a.m. and 6:59 a.m. The study outcomes were death; bronchopulmonary dysplasia, retinopathy of prematurity, and severe (grade 3 or 4) intraventricular hemorrhage among survivors; the composite of each morbidity or mortality; and the composite of death or 1 or more of the evaluated morbidities.

Of 47 617 evaluated infants, 9317 (19.6%) were born during off-peak hours. The frequencies of all study outcomes were higher among infants born during off-peak compared with peak hours. After adjusting for maternal, infant, and hospital characteristics, off-peak hour delivery was associated with increased odds of severe intraventricular hemorrhage among survivors (OR 1.39, 95% CI 1.23-1.57) and the composite outcomes of death or severe intraventricular hemorrhage (OR 1.16, 95% CI 1.07-1.25) and death or major morbidity (OR 1.08, 95% CI 1.02-1.15). There was no evidence of subgroup effects based on delivery mode, birth hospital neonatal intensive care level or annual very low birth weight infant delivery volume, or weekday vs weekend off-peak hour delivery for any study outcome.

Very low birth weight infants born between midnight and 7:00 a.m. are at increased risk for severe intraventricular hemorrhage and death or major neonatal morbidity.