Modified model displaying the collapsed non-significant strata (1–12) from table 2 into new strata (A–G)
| Group (group in table 2) | Oxytocin augmentation* | Episiotomy* | Operative vaginal delivery* | Birth weight† | Women N | OASI‡ N (%) | OR | aOR (95% CI) |
|---|---|---|---|---|---|---|---|---|
| A (1,2) | − | +/− | − | − | 6762 | 258 (3.8) | 1.0 | 1.0 |
| B (7,8) | + | +/− | − | − | 3660 | 209 (5.7) | 1.5 | 1.8 (1.5 to 2.2) |
| C (3,5) | +/− | + | + | − | 1820 | 135 (7.4) | 2.0 | 2.3 (1.8 to 2.8) |
| D (4,6) | +/− | − | + | − | 1212 | 150 (12.4) | 3.6 | 4.1 (3.3 to 5.1) |
| E (9–10) | +/− | +/− | − | + | 1395 | 144 (10.3) | 2.9 | 3.1 (2.5 to 3.9) |
| F (11) | +/− | + | + | + | 393 | 55 (14.0) | 4.1 | 4.7 (3.4 to 6.5) |
| G (12) | +/− | − | + | + | 234 | 62 (26.5) | 9.1 | 10.5 (7.6 to 14.4) |
Unadjusted OR, adjusted (aOR) and 95% CIs after adjusting for epidural analgaesia.
*Used (+)/unused (−).
†≥4000 g (+)/<4000 g (−).
‡Obstetric anal sphincter injury.