Risk factor analysis including cases and controls
| Primiparous women | Multiparous women | |||
| OR (95% CI) | AOR (95% CI)* | OR (95% CI) | AOR (95% CI)† | |
| Maternal age | ||||
| <30 | Ref | Ref | Ref | Ref |
| 30–34 | 8.0 (2.6 to 24.9) | 6.3 (2.0 to 20.0) | 1.7 (1. to 2.7) | 1.7 (0.9 to 3.2) |
| 35–39 | 11.0 (3.5 to 34.9) | 7.0 (2.1 to 23.6) | 3.1 (2.0 to 4.8) | 2.7 (1.4 to 5.2) |
| ≥40 | 30.7 (8.2 to 115.9) | 19.1 (4.6 to 80.3) | 3.1 (1.6 to 6.0) | 2.0 (0.8 to 5.0) |
| Body mass index (kg/m2) | ||||
| <25 | Ref | Ref | Ref | Ref |
| 25–29.9 | 1.2 (0.6 to 2.6) | 1.4 (0.6 to 3.2) | 1.1 (0.7 to 1.8) | 0.8 (0.4 to 1.4) |
| ≥30 | 0.7 (0.3 to 2.0) | 0.7 (0.2 to 2.2) | 1.4 (0.9 to 2.1) | 0.8 (0.5 to 1.4) |
| Smoking during pregnancy | 0.2 (0.1 to 1.0) | 0.4 (0.1 to 1.8) | 1.3 (0.9 to 2.0) | 1.3 (0.7 to 2.4) |
| Number of previous caesarean births | ||||
| No prior caesarean delivery | n.a | n.a | Ref | Ref |
| 1 | n.a | n.a | 5.8 (3.7 to 9.1) | 3.7 (2.2 to 6.3) |
| ≥2 | n.a | n.a | 24.8 (14.3 to 43.1) | 13.8 (7.4 to 26.1) |
| Placenta praevia during pregnancy | 9.6 (2.2 to 41.9) | 3.0 (0.6 to 15.2) | 64.9 (25.9 to 162.5) | 36.3 (14.0 to93.7) |
| Multiple pregnancy | 14.2 (3.5 to 57.2) | 6.1 (1.1 to 34.1) | 1.1 (0.4 to 2.7) | 1.5 (0.5 to 4.9) |
| Assisted conception | 5.4 (2.2 to 13.1) | 1.5 (0.5 to 5.1) | 4.4 (1.4 to 13.7) | 2.6 (0.6 to 11.2) |
*Adjusted for maternal age, body mass index, smoking, placenta praevia during pregnancy, multiple pregnancy and assisted conception.
†Adjusted for maternal age, body mass index, smoking, number of previous caesarean deliveries, placenta praevia during pregnancy, multiple pregnancy and assisted conception
AOR, adjusted OR; n.a., not applicable; Ref, reference value.