Birth during off-hours: Impact of time of birth, staff´s seniority, and unit volume on maternal adverse outcomes-a population-based cross-sectional study of 87 065 deliveries.

BACKGROUND: The aim of this study was to investigate whether time of birth, unit volume, and staff seniority impact the incidence of maternal complications in deliveries ≥34 + 0 gestational weeks. METHODS: We conducted a population-based cross-sectional study of 87 065 deliveries occurring between 2004 and 2015 in ten public hospitals in Styria, Austria. A composite adverse maternal outcome measure of uterine atony, postpartum hysterectomy, postpartum bleeding, impaired wound healing, postpartum infections requiring antibiotic treatment, sepsis, or maternal death was used to compare outcomes by time of birth, unit volume, and staff seniority. Based on delivery data, generalized estimating equations (GEEs) were used to calculate the risk of maternal adverse outcomes. RESULTS: Maternal adverse events occurred in 1.33% of deliveries. Incidence of maternal adverse events was highest for units with >1000 deliveries (adjusted OR 1.40; CI 95%: 1.16-1.69) and higher for perinatal centers (adjusted OR 1.35; CI 95%: 1.15-1.57) compared with reference units (500-1000 deliveries/year). Delivery during the daytime compared with the afternoon and nighttime did not affect the incidence of maternal complications (P = 0.765 and P = 0.136, respectively). Compared with resident-guided deliveries, the odds ratio for an adverse event was the same when a consultant attended the delivery (adjusted OR 1.13; CI 95%: 0.98-1.30) but lower in deliveries managed by midwives only (adjusted OR 0.21; CI 95%: 0.07-0.64). CONCLUSION: Procedures performed during the night shift were not associated with increased complication rates. Delivery volume and high-volume centers were associated with the highest risk of maternal complications, and units with 500-1000 deliveries per year were the lowest. With increasing odds of pregnancy risks, these results change, and delivering in a high-volume center becomes at least as safe as delivering in a smaller unit.