Role of mediolateral or lateral episiotomy in preventing obstetric anal sphincter injury (OASI) in nulliparous women undergoing vacuum-assisted delivery: A systematic review and meta-analysis

Background The potential preventive effect of mediolateral and lateral episiotomy on the risk of anal sphincter injury related to vacuum delivery in nullipara has been reported by different well-designed studies in the last years. Objectives The aim of this systematic review and meta -analysis is to summarize the available evidence on the protective effect of mediolateral or lateral episiotomy towards the occurrence of obstetric anal sphincter injury (OASI) in nulliparous women who were submitted to vacuum-assisted delivery. Search strategy: PubMed, Embase, CINAHL, Cochrane Library and Scopus databases were retrospectively searched without any temporal restriction up to March 1st 2025. Selection criteria: Randomized controlled trials, retrospective, prospective case-control or cohort studies investigating the incidence of perineal tears involving anal sphincter muscles and/or rectal mucosa after vacuum-assisted birth with and without mediolateral/lateral episiotomy in nulliparous women were included. Data collection and analysis: Risk of bias assessment was conducted for each included study by applying ROB2 score for RCTs and ROBINS-I score for non-randomized studies. Data were extracted and analyzed with Review Manager 5.4.1, results were reported by means of pooled Odd-ratios (ORs) and presented as Forest plots. Main results: 31 studies (3 RCTs and 28 non-randomized studies) were included. Cumulative sample size consisted in 608,359 nulliparous women who were submitted to vacuum-assisted delivery. Mediolateral/lateral episiotomy was found to halve the incidence of OASI (OR 0.56 [95 % CI 0.42–0.73]) with high between-study heterogeneity reported (I 2 = 99 %). At sensitivity analysis, a significant reduction in OASI incidence in case of mediolateral/lateral episiotomy was confirmed (OR 0.58 [95 %CI 0.44–0.78]); this analysis was conducted on low/moderate risk of bias studies (1RCT e 5 non-randomized studies, 15,799 patients) and associated with low heterogeneity (I 2 = 42 %). Conclusions This updated meta -analysis on the role of mediolateral/lateral episiotomy in nulliparous women submitted to vacuum assisted delivery confirms its protective role from OASI.