Episiotomy is associated with a reduced risk of obstetric anal sphincter injury in nulliparous vacuum‐assisted deliveries, particularly in high‐risk cases

Abstract Introduction Vacuum‐assisted delivery is a major risk factor for obstetric anal sphincter injury (OASI), yet agreement is lacking on whether mediolateral episiotomy mitigates risk. The objective of this study was to evaluate whether episiotomy during vacuum‐assisted delivery in nulliparous women affects the risk of OASI and to identify subgroups who may benefit from it. Material and Methods A retrospective cohort study including all nulliparous singleton pregnancies delivered by vacuum‐assisted delivery at a tertiary center (January 2011–December 2022). Twin deliveries and multiparous women were excluded. Mediolateral episiotomy was performed according to the physician's preference and clinical judgment. The primary outcome was the risk of OASI. The diagnosis of OASI was based on a clinical assessment immediately after delivery. Multivariable logistic regression was used to assess the association between mediolateral episiotomy and OASI while adjusting for potential confounders: maternal age, prepregnancy BMI, gestational age, prolonged second stage, occiput posterior, and epidural analgesia. Results Among 7951 vacuum‐assisted deliveries, 7201 (90.6%) had an episiotomy and 750 (9.4%) did not. The groups were similar, though episiotomy cases more often had a prolonged second stage (32.0% vs 25.9%, p  = 0.001), occiput posterior (12.7% vs 9.6%, p  = 0.03), and birthweight ≥3500 g (25.4% vs 21.7%, p  = 0.03). OASI occurred twice as often without episiotomy (2.8% vs 1.4%, p  = 0.01). After adjustment, episiotomy remained (adjusted odds ratio 0.42, 95% CI 0.25–0.70). The number needed to treat (NNT) with episiotomy to prevent one OASI was 64 overall, and was lower in the presence of intrapartum risk factors: 16 with prolonged second stage, 33 with occiput posterior, and 27 when birthweight exceeded 3500 g. Postpartum hemorrhage requiring transfusion occurred more frequently with episiotomy (3.9% vs 1.5%; p  = 0.001), corresponding to a number needed to harm (NNH) of 43. Neonatal outcomes did not differ significantly. Conclusions In nulliparous women, mediolateral episiotomy during vacuum‐assisted delivery was associated with a 50% reduction in OASI. The preventive effect of mediolateral episiotomy was greater when multiple intrapartum risk factors were present.