Time of Birth and Risk of Neonatal Death at Term: Retrospective Cohort Study

Abstract

It is unclear whether the day and time of birth have an independent effect on the risk of perinatal death. The results of previous studies examining this possible relationship have been inconsistent. A finding of significant variation in the risk of neonatal death outside the normal working week would suggest that improvements in the level of clinical services provided out of hours may be an effective strategy to reduce rates of perinatal death. This population-based retrospective cohort study was designed to investigate the possible effect of the time and day of birth on the risk of neonatal death at term. Data on singleton births from the Scottish morbidity records for 1985–2004 were linked to the Scottish Stillbirth and Infant Death Survey, and a birth certificate database. Records on 1,039,560 live-born term infants in cephalic presentation were examined. Perinatal deaths from multiple pregnancy, stillbirths, and congenital abnormalities were excluded. The primary study outcome measure was neonatal death (unrelated to congenital anomalies) and a subgroup of deaths ascribed to intrapartum anoxia. The normal working week was defined as Monday to Friday, 09:00 to 17:00 hours; all other times were out of hours. A total of 539 (0.05%) neonatal deaths were identified in the study cohort (5.2 per 10,000 live births; about half of these deaths were ascribed to intrapartum anoxia (n = 273, 51%). The risk of neonatal death during the normal working week was 4.2 per 10,000 live births, and risk of death at all other times was 5.6 per 10,000 live births; the unadjusted odds ratio (OR) was 1.3, with a 95% confidence interval (CI) of 1.1 to 1.6. Adjustment for confounding effects of maternal characteristics did not change the results. The higher rate of neonatal death out of hours appeared to result from significant excess risk of death ascribed to intrapartum anoxia (unadjusted OR, 1.7; 95% CI, 1.3–2.3) and was similar in multivariate analysis. Exclusion of elective cesarean deliveries from the analysis attenuated the association between delivery out of hours and the risk of anoxia-related death, but the association persisted (adjusted OR, 1.5; 95% CI, 1.1–1.9; P < 0.05). With exclusion of births by elective cesarean, the attributable fraction of neonatal deaths ascribed to intrapartum anoxia associated with delivery out of hours was 25.9% (95% CI, 4.8%–42.3%). These findings show that the risk of neonatal death at term ascribed to anoxia is increased among women delivering outside the hours of the normal working week. The investigators suggest that the overall rates of perinatal death could be reduced by improving the level of clinical care for women delivering out of normal working hours.