Time of birth and risk of neonatal death at term: retrospective cohort study

Objective To determine the effect of time and day of birth on the risk of neonatal death at term. Design Population based retrospective cohort study. Setting Data from the linked Scottish morbidity records, Stillbirth and Infant Death Survey, and birth certificate database of live births in Scotland, 1985-2004. Subjects Liveborn term singletons with cephalic presentation. Perinatal deaths from congenital anomalies excluded. Final sample comprised 1 039 560 live births. Main outcome measure All neonatal deaths (in the first four weeks of life) unrelated to congenital abnormality, plus a subgroup of deaths ascribed to intrapartum anoxia. Results The risk of neonatal death was 4.2 per 10 000 during the normal working week (Monday to Friday, 09001700) and 5.6 per 10 000 at all other times (out of hours) (unadjusted odds ratio 1.3, 95% confidence interval 1.1 to 1.6). Adjustment for maternal characteristics had no material effect. The higher rate of death out of hours was because of an increased risk of death ascribed to intrapartum anoxia (adjusted odds ratio 1.7, 1.2 to 2.3). Though exclusion of elective caesarean deliveries attenuated the association between death ascribed to anoxia and delivery out of hours, a significant association persisted (adjusted odds ratio 1.5, 1.1 to 2.0). The attributable fraction of neonatal deaths ascribed to intrapartum anoxia associated with delivery out of hours was 26% (95% confidence interval 5% to 42%). Conclusions Delivering an infant outside the normal working week was associated with an increased risk of neonatal death at term ascribed to intrapartum anoxia.