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.