Association of timing of birth with mortality among preterm infants born in Canada

To assess the association between time of birth and mortality among preterm infants. Population-based study of infants born 22–36 weeks gestation (GA) in Canada from 2010 to 2015 (n = 173 789). Multivariable logistic regression models assessed associations between timing of birth and mortality. Among infants 22–27 weeks GA, evening birth was associated with higher mortality than daytime birth (adjusted odds ratio [AOR] 1.14, 95% CI 1.01–1.29). Among infants 28–32 weeks GA and 33–36 weeks GA, night birth was associated with lower mortality than daytime birth (AOR 0.75, 95% CI 0.59–0.95; AOR 0.78, 95% CI 0.62–0.99, respectively). Sensitivity analysis excluding infants with major congenital anomaly revealed that associations between hour of birth and mortality among infants born 28–32 and 33–36 weeks GA decreased or were not statistically significant. Higher mortality among extremely preterm infants during off-peak hours may suggest variations in available resources based on time of day.