Episiotomy and Anal Sphincter Injury During Operative Vaginal Delivery in a U.S. Cohort

OBJECTIVE: To evaluate the association between episiotomy and obstetric anal sphincter injury during operative vaginal delivery (OVD) in a diverse, modern U.S. cohort. METHODS: This was a secondary analysis of patients who had OVD of a term, cephalic singleton neonate in the MFMU APEX (Maternal-Fetal Medicine Units Assessment of Perinatal Excellence) cohort. The primary outcome was obstetric anal sphincter injury defined as a third- or fourth-degree perineal laceration, and the exposure was episiotomy. Multivariable logistic regression adjusted for length of the second stage of labor, maternal age, body mass index (BMI), and birth weight. We tested for interaction in the association between episiotomy type and obstetric anal sphincter injury by OVD type and vaginal delivery history. RESULTS: Among 5,277 participants, 3,453 had vacuum-assisted vaginal delivery and 1,824 had forceps-assisted vaginal delivery. Episiotomy was performed in 1,704 deliveries (32.3%) (n=1,301 midline, n=384 mediolateral, n=19 unknown type). Obstetric anal sphincter injury incidence was 20.1% (95% CI, 19.0–21.2). As a main effect, odds of obstetric anal sphincter injury were higher among patients with episiotomy compared with those with no episiotomy (adjusted odds ratio 1.45, 95% CI, 1.25–1.67). There was a significant interaction between type of episiotomy and obstetric anal sphincter injury by OVD type ( P <.001) and by vaginal delivery history ( P =.02); in this model, midline episiotomy during vacuum-assisted vaginal delivery compared with no episiotomy was associated with higher odds of obstetric anal sphincter injury for patients with or without prior vaginal delivery, and mediolateral episiotomy was associated with lower odds of obstetric anal sphincter injury for patients without prior vaginal delivery for both vacuum-assisted and forceps-assisted vaginal delivery. CONCLUSION: Mediolateral episiotomy was associated with lower odds of obstetric anal sphincter injury for patients without previous vaginal delivery undergoing OVD. In contrast, midline episiotomy was associated with increased odds of obstetric anal sphincter injury for vacuum-assisted vaginal delivery regardless of vaginal delivery history. These findings are consistent with several previous studies conducted in settings with different baseline rates of OVD and episiotomy and suggest that further investigation is warranted to identify patients who may derive benefit from mediolateral episiotomy before OVD.