Context

It has long been suspected that the risk of adverse obstetrical outcomes is higher with births at night and on the weekend, when medical staff are usually less plentiful and, on average, less experienced. Published reports examining the impact of hour and day of birth on neonatal mortality have had inconsistent findings, with some showing higher mortality after night and weekend births and others showing no difference. The reasons for these inconsistent findings are not clear but may include variation in staffing and available services in the hospitals studied; approaches to analysis, including patients excluded; and the use of insufficient or inappropriate study populations.