Risk Factors for Intrapartum Anorectal Mucosal Lacerations and Rectovaginal Fistula: A Retrospective Comparative Study.

Introduction:We examined the risk factors for fourth-degree perineal lacerations (intrapartum anorectal mucosal lacerations) and rectovaginal fistulas as one of the later complications. Methods:We reviewed the obstetric records of all singleton vaginal deliveries after 22 weeks of gestation at our institute between January 2006 and December 2018 (n = 19,370). Results:Of the 19,370 deliveries, 61 had fourth-degree perineal lacerations (0.31%). Of the 61 women, 5 (8.2%) developed rectovaginal fistulas 2-3 weeks after their deliveries. Upon multivariate analysis, nulliparity (Adjusted odds ratios (OR) 3.58, 95% confidence interval (CI) 1.6-8.1, p < 0.01), midline episiotomy (Adjusted OR 2.10, 95% CI 1.0-4.2, p = 0.03), vacuum extraction (Adjusted OR 7.01, 95% CI 3.5-14, p < 0.01), and forceps delivery (Adjusted OR 22.0, 95% CI 7.8-61, p < 0.01) were independently associated with fourth-degree perineal lacerations, while mediolateral episiotomy (Adjusted OR infinity, 95% CI 2.1-infinity, p = 0.03) and forceps delivery (Adjusted OR infinity, 95% CI 14.5-infinity, p = 0.01) were independently associated with rectovaginal fistulas. In addition, in the women with fourth-degree perineal lacerations, mediolateral episiotomy was associated with rectovaginal fistulas (OR infinity, 95% CI 1.8-infinity, p = 0.04). Conclusions:Midline episiotomy and instrument-assisted delivery are independent risk factors for fourth-degree perineal lacerations after vaginal delivery. Mediolateral episiotomy and forceps delivery were independently associated with rectovaginal fistulas. Once fourth-degree perineal lacerations occurred, women with mediolateral episiotomies were more likely to develop rectovaginal fistulas.