Episiotomy use among vaginal deliveries and the association with anal sphincter injury: a population-based retrospective cohort study

BACKGROUND: The rate of obstetric anal sphincter injury has increased in recent years, particularly among operative vaginal deliveries. We sought to characterize temporal trends in episiotomy use and to quantify the association between episiotomy and obstetric anal sphincter injury. METHODS: Using a population-based retrospective cohort study design of hospital data from 2004 to 2017, we studied all vaginal deliveries of singleton infants at term gestation in Canada (excluding Quebec). Rates of obstetric anal sphincter injury were contrasted between women who had an episiotomy and those who did not. Log-binomial regression was used to estimate the association between episiotomy and obstetric anal sphincter injury among women with spontaneous and operative vaginal deliveries after controlling for confounders. RESULTS: The study population included 2 570 847 deliveries. Episiotomy use declined significantly among operative vaginal deliveries (53.1% in 2004 to 43.2% in 2017, p < 0.0001) and spontaneous vaginal deliveries (13.5% in 2004 to 6.5% in 2017, p < 0.0001). Episiotomy was associated with higher rates of obstetric anal sphincter injury among spontaneous vaginal deliveries (4.8 with episiotomy v. 2.4% without; adjusted rate ratio [RR] 2.06, 95% confidence interval [CI] 2.00-2.11) and this association remained after stratification by parity and obstetric history. In contrast, episiotomy was associated with lower rates of obstetric anal sphincter injury among forceps deliveries in nulliparous women (adjusted RR 0.63, 95% CI 0.61-0.66), and women with vaginal birth after cesarean (adjusted RR 0.71, 95% CI 0.60-0.85), but not among parous women without a previous cesarean (adjusted RR 1.16, 95% CI 1.00-1.34). INTERPRETATION: Episiotomy use has declined in Canada for all vaginal deliveries. The protective association between episiotomy and obstetric anal sphincter injury among women who gave birth by operative vaginal delivery (especially forceps) warrants reconsideration of clinical practice among nulliparous women and those attempting vaginal birth after cesarean.