Factors associated with an increased risk of instrumental vaginal delivery in women with epidural analgesia for labour A retrospective cohort study

BACKGROUND Epidural analgesia is the most effective form of labour analgesia, but is associated with an increased risk of instrumental delivery. OBJECTIVE To evaluate factors that are associated with an increased risk of instrumental delivery. DESIGN Retrospective cohort data study. SETTING Singapore's major public maternity institution. PATIENTS All obstetric patients who received labour epidural analgesia for vaginal delivery between January 2012 to December 2015. INTERVENTION None. MAIN OUTCOME MEASURES Our primary outcome was the incidence of instrumental delivery. RESULTS Out of 17 227 pregnant women who received labour epidural analgesia, 12% (n = 2069) had instrumental delivery. Independent factors associated with an increased risk of instrumental delivery included maternal factors [nulliparity (adjusted odds ratio (aOR) 2.97, 95% CI 2.61 to 3.39, P < 0.0001] and advanced maternal age (aOR 1.04, 95% CI 1.03 to 1.05, P < 0.0001)). Greater maternal height (aOR 0.18, 95% CI 0.08 to 0.40), P < 0.0001) was associated with a reduced risk of instrumental delivery. Significant labour-related factors increasing the risk of an instrumental delivery were the use of prostin (aOR 1.19, 95% CI 1.07 to 1.32, P = 0.0014), pre-epidural analgesia (aOR 1.16, 95% CI 1.05 to 1.28, P = 0.0040), a longer second stage of labour (aOR 1.23, 95% CI 1.20 to 1.26, P < 0.0001), higher infant birth weight (aOR 1.27, 95% CI 1.12 to 1.43, P = 0.0002) and an epidural performed by a senior anaesthetist (aOR 1.94, 95% CI 1.72 to 2.18, P < 0.0001). Labour epidural-related factors for an increased risk of instrumental delivery were the occurrence of breakthrough pain (aOR 1.55, 95% CI 1.37 to 1.76, P < 0.0001), a more dense motor block (aOR 1.14, 95% CI 1.03 to 1.25, P = 0.0097) and having an epidural infusion stopped at full cervical dilatation (aOR 1.18, 95% CI 1.05 to 1.32, P = 0.0048) [receiver operating characteristic (ROC) = 0.75]. CONCLUSIONS The multivariate model generated would help identify women at higher risk of instrumental delivery, which can help clinicians to address potentially modifiable factors and improve clinical care.