Birth Outcomes Associated With Assisted Vaginal Birth in an Occipito‐Posterior Position: Secondary Analyses of a Randomised Controlled Trial and Cohort Study

To investigate the morbidity associated with assisted vaginal birth (AVB) and an occipito-posterior (OP) fetal head position. Observational study based on secondary analyses of a randomised controlled trial and cohort study. Two university affiliated maternity hospitals in Ireland. A combined cohort of 1081 nulliparous women at term who were assessed for AVB in the second stage of labour. Univariable and multivariable logistic regression analyses were performed. Postpartum haemorrhage (PPH), obstetric anal sphincter injury (OASI), fetal acidosis, neonatal trauma, failed or abandoned AVB leading to caesarean section (CS). Of the 1081 AVBs, a total of 192 (17.8%) had an OP position at the outset, with 103 of these (53.6%) rotated to occipito-anterior (OA) prior to AVB and 89 (46.4%) remaining OP. AVB completed in a non-rotated OP position compared with OP rotated to OA was associated with an increased risk of PPH (34% 30/89 vs. 15% 15/103, adjusted Odds Ratio (adj OR) 3.57; 95% Confidence Interval (CI) 1.68 to 7.58), OASI (16% 14/65 vs. 2% 2/98, adj OR: 12.62; 95% CI: 2.65 to 60.12) and CS (27% 24/89 vs. 5% 5/103, adj OR: 8.99; 95% CI: 3.14 to 25.74). There were no significant differences in neonatal outcomes. The diagnosis of OP was incorrectly assigned as either OA or occipito-transverse (OT) in 35 of the 192 cases (18.2%). This study highlights the associated morbidity when attempting an AVB with a non-rotated OP position rather than rotating to OA.