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.