Time of birth and the risk of neonatal death.

OBJECTIVE: To assess whether mortality is increased in the United States in infants born at night, we compared case-mix adjusted neonatal mortality for low- and high-risk infants born during the daytime (7 am to 6 pm), early night (7 pm to 12 am), and late night (1 am to 6 am).
METHODS: California linked birth-death certificate data on 3,363,157 infants, weighing more than 500 g and born without lethal congenital anomalies in 1992-1999, were analyzed. Logistic regression, adjusting for birth weight, gender, prenatal care initiation, maternal hypertension, eclampsia, diabetes, and placental abruption/previa, was used to estimate the relationship between neonatal mortality and time of birth.
RESULTS: The overall neonatal mortality was 2.08 deaths per 1,000 live births. Neonatal mortality was 1.88 for daytime births, increasing to 2.37 for early night and 2.31 for late night births. After adjusting for case mix, early night births had a 12% increase and late night births a 16% increase in the odds of neonatal death, an excess that accounts for 9.6% of all neonatal deaths. Mortality was increased for night births that were less than 1,500 g or more than 1,500 g, singletons or multiples, and those delivered vaginally or by cesarean. The increased risk was identified in hospitals that provide intermediate, community, and regional neonatal intensive care, but not in hospitals that provide primary care.
CONCLUSION: Identifying the causal factors and reducing the increased burden of mortality for infants born at night should be a major priority for perinatal medicine.