Fig. 2

Adjusted OR (aOR) and 99% confidence intervals (CIs) of unplanned SC, instrumental delivery, induction of labour and epidural analgesia categorised by daily delivery volume (quiet vs. busy day) in five delivery hospital categories.

C1 = Delivery hospitals with < 1000 annual deliveries. C2 = Delivery hospitals with 1000–1999 annual deliveries C3 = Delivery hospitals with 2000–2999 annual deliveries. C4 = Delivery hospitals with ≥3000 annual deliveries. C5 = University hospitals. Unplanned CS=Unplanned caesarean section. EA = Epidural analgesia. Quiet days = the number of deliveries that occurred during the closest 10% of the lowest daily delivery volume days. Optimal days = the number of deliveries occurred between the lowest (10%) and highest (10%) delivery volume days. Busy days = the number of deliveries that occurred during the closest 10% of the highest daily delivery volume days. aOR adjusted by maternal age (categorical), parity (nulliparous or multiparous), birth weight (categorical). ** p < 0.05. *** p < .001