Adjusted rate ratios expressing the association between episiotomy and obstetric anal sphincter injury among term singleton vaginal deliveries with information on parity, Canada, 2004–2017
| Type of delivery | Nulliparous | Parous | |||||||
|---|---|---|---|---|---|---|---|---|---|
| No previous CD | VBAC | ||||||||
| OASI rate (%) | ARR* (95% CI) | OASI rate (%) | ARR* (95% CI) | OASI rate (%) | ARR* (95% CI) | ||||
| Episiotomy No | Episiotomy Yes | Episiotomy No | Episiotomy Yes | Episiotomy No | Episiotomy Yes | ||||
| All vaginal deliveries | 6.7 | 10.9 | 1.57 (1.55–1.60) | 1.3 | 4.3 | 3.12 (2.99–3.25) | 5.7 | 11.6 | 2.03 (1.90–2.18) |
| SVD | 4.7 | 6.0 | 1.25 (1.21–1.28) | 1.1 | 2.9 | 2.55 (2.42–2.69) | 4.1 | 7.2 | 1.77 (1.58–1.97) |
| OVD | 17.0 | 15.7 | 0.90 (0.88–0.93) | 5.2 | 9.2 | 1.83 (1.71–1.96) | 16.2 | 16.5 | 1.03 (0.93–1.13) |
| Forceps | 28.4 | 18.7 | 0.63 (0.61–0.66) | 10.6 | 11.4 | 1.16 (1.00–1.34) | 26.8 | 19.1 | 0.71 (0.60–0.85) |
| Vacuum | 13.8 | 12.7 | 0.88 (0.85–0.91) | 4.4 | 7.6 | 1.71 (1.57–1.87) | 13.5 | 13.7 | 1.00 (0.88–1.14) |
| Sequential | 33.8 | 24.4 | 0.66 (0.60–0.72) | 14.4 | 18.9 | 1.51 (1.18–1.92) | 32.2 | 25.9 | 0.70 (0.47–1.05) |
Note: ARR = adjusted rate ratio, CD = cesarean delivery, CI = confidence interval, OASI = obstetric anal sphincter injury, OVD = operative vaginal delivery, SVD = spontaneous vaginal delivery, VBAC = vaginal birth after cesarean.
↵* The reference group included deliveries without episiotomy within each respective delivery group; i.e., reference group for forceps deliveries among nulliparous women included forceps deliveries without episiotomy among nulliparous women.
Models adjusted for maternal age, labour induction, prolonged second stage of labour, epidural anesthesia, infant birth weight, province and year of birth.