Objectives
To assess the impact of occipito‐posterior position in the second stage of labour on operative delivery.

Methods
Double‐blinded prospective cohort study of ultrasound determined occiput‐posterior position during the second stage of labour compared with occiput‐anterior position. The primary outcome was operative (caesarean section, forceps or vacuum) delivery.

Results
A total of 68% (13/19) women in the occiput‐posterior group, and 27% (39/141) in the occiput‐anterior group had an operative delivery (unadjusted: P < 0.001). Caesarean section was performed in 37% and 5%, respectively (P < 0.001). The occiput‐posterior group had a longer second stage (mean 2 h 59 minutes vs 1 h 54 minutes; P = 0.001) and larger infants (mean 3723 g vs 3480 g, P = 0.024). In the logistic regression, occiput‐posterior position, nulliparity, abnormal second stage cardiotocograph and epidural analgesia were independent predictors for operative delivery. Conclusions Occiput‐posterior position early in the second stage of labour is strongly associated with operative delivery. There is potential to explore interventions such as manual rotation.