Time of birth and delivery outcomes: a retrospective cohort study.

Studies performed previously have attributed increased risk of intrapartum anoxia to delivery outside the normal working week. We sought to determine if the time of delivery effects outcome with respect to delivery characteristics and neonatal condition at birth. We identified a cohort of 14,426 deliveries over a 3-year period. These were analysed as three groups: night (00:00-07:59); day (08:00-15:59) and twilight (16:00-23:59). We found significantly more deliveries at night 36.3% (n = 5,240; p =0.01). At night, there were non-significantly more 'normal' deliveries compared with during the day and twilight hours (78.4%, 76.2%, 77.3%, respectively; p = 0.27). The caesarean section rate did not differ significantly between the groups (14.2%, 15.6%, 14.8%; p = 0.147). There were significantly fewer assisted deliveries in the night-time period (6.6%, 8.0%, 7.3%; p = 0.03). Women who delivered at night were more likely to have a normal delivery and less likely to have obstetric intervention in the form of assisted or operative delivery. There were no significant differences in the need for resuscitation to be performed at birth across the three groups (14.3%, 13.3%, 14.8%; p = 0.111). There was no significant difference in the numbers of babies directly admitted to the neonatal intensive care unit (NICU) (5.9%, 6.8%, 6.3%; p = 0.198) in the three respective time periods.