Busy day effect on intrapartum adverse maternal outcomes - a population-based study of 601 247 singleton deliveries.

Background: This was a retrospective population-based study, utilizing the data of 601 247 singleton hospital deliveries collected from the Finnish Medical Birth Register (MBR) in 2006-2016. The aim of this study was to analyse the busy day effect on intrapartum adverse maternal outcomes.

Methods: To implement the study design, daily delivery frequencies and ranges (min-max) for each delivery unit (n = 26) were stratified to the daily delivery volume distributions by the delivery unit's annual delivery volume and profile: Category (C)1 < 1000, C2 1000-1999, C3 2000-2999, C4 ≥ 3000 and C5 the profile of university hospitals. To study the busy day effect, the quiet, optimal and busy days were defined by calculating the number of days (%) with the lowest and highest daily delivery frequencies and summed to the nearest 10 % in each hospital category. Optimal days were determined by calculating approximately 80 % of deliveries occurring between the lowest 10 %, and highest 10 % in each hospital category. Crude and adjusted odd ratios (ORs) with 99 % confidence intervals (CIs) were used to analyze the busy day effect on adverse maternal outcomes, blood transfusions, manual removal of the placenta and obstetric anal sphincter injuries, separately in each hospital category.

Results: The busy day effect was associated with the 28 % (99 % CI 8-52 %) and 25 % (99 % CI 11-40 %) increased need for blood transfusions in C2 and university hospitals (C5), respectively, whereas 22 % (99 % CI 10-31 %) less blood transfusions were needed at university hospitals during quiet days. In C3 hospitals, 83 % (99 % CI 65-92 %) less blood transfusions were needed during busy days. Obstetric and anal sphincter injury rates declined during quiet days by 22 % (99 % CI 3-38 %) only in university hospitals.

Conclusions: The findings of this study identify no specific pattern to the busy day effect for adverse maternal outcomes defined as manual removal of the placenta or obstetric and anal sphincter injuries. However, both quiet and busy days seem to be associated with increased or decreased need for blood transfusions in different sized delivery units. Findings also suggest that quiet days are associated with a decreased number of obstetric and anal sphincter injuries.