Interpretation We found no significant associations between time of OVD and maternal and neonatal morbidities. This is consistent with two previous studies.20 21 The US Maternal-Fetal Medicine Units Network Cesarean Registry found no association between change of shift for physicians

and maternal or neonatal morbidity following an unscheduled ATM inhibitor clinical trial CS.20 Another US study found no difference in timing of birth and resident duty-hour restrictions on outcomes for small preterm infants.21 However, a recent retrospective cohort study in the Netherlands found that evening (18:00–22:59) and night-time (23:00–07:59) deliveries requiring obstetric interventions or labour augmentation were associated with increased perinatal morbidity and mortality.13 Another retrospective study evaluating neonatal morbidity in an unselected population found increased rates of emergency CS and NICU admission during the hours of 23:00 and 03:00.14 Varying study designs, obstetric environments and limited ability to control for confounding factors may have contributed to the conflicting findings. We found a higher rate of shoulder dystocia during the day, which was unexpected but may reflect our policy of prioritising

inductions of labour for pregnancies with suspected macrosomia and diabetes early in the day. Operator inexperience has been linked to excessive number of pulls at OVD, use of multiple instruments and CS for failed OVD, all of which increase the risk of trauma to the mother and neonate.8 22–25 It was perhaps surprising that there was no evidence of excess morbidity at night, even though a greater proportion of deliveries were performed by mid-grade operators with access to a consultant but in most cases no direct supervision. It was also notable that the mean decision-to-delivery intervals were under 15 min in both time periods.26 Our findings suggest that consultant support was available when necessary

and that the travel time associated with attendance from home did not compromise patient care. Fewer OVDs were completed by mid-grade operators during the day, which was directly related to a higher proportion of daytime deliveries performed by junior operators. From a training perspective, it GSK-3 is essential that obstetricians have opportunities for both direct and indirect supervision in order to develop clinical decision-making skills and this appears to happen for mid-grade operators more often at night. The overall complement of staff available at night is another important consideration. The obstetric staffing for a unit of this size falls below the recommended levels described by the RCOG.27 This is probably the case for many units in the UK and Ireland.