Table 3. Risk estimates for spontaneous preterm birth according to some maternal obstetric history, comparing women who delivered prematurely (CASES) and women who delivered at term (CONTROLS).
| Obstetric history | CASES | CONTROLS | OR* (95% CI) |
| n (%) | n (%) | ||
| Parity | |||
| • Nulliparous | 1305 (48.7) | 527 (46.0) | 0.89 (0.63–1.26) |
| • 1–2 deliveries | 1021 (38.1) | 491 (42.8) | 0.75 (0.55–1.03) |
| • ≥3 deliveries | 355 (13.2) | 128 (11.2) | Ref. |
| Previous caesarean section* | |||
| • No | 1094 (70.0) | 416 (62.4) | Ref. |
| • Yes | 469 (30.0) | 251 (37.6) | 0.71 (0.61–0.83) |
| Previous abortion* | |||
| • No | 956 (61.2) | 435 (65.2) | Ref. |
| • Yes | 607 (38.8) | 232 (34.8) | 1.19 (0.99–1.43) |
| Previous uterine curettage* | |||
| • No | 1146 (73.6) | 500 (75.2) | Ref. |
| • Yes | 411 (26.4) | 165 (24.8) | 1.09 (0.85–1.38) |
| Inter-pregnancy interval * | |||
| • >12 months | 1394 (90.5) | 622 (94.8) | Ref. |
| • ≤12 months | 146 (9.5) | 34 (5.2) | 1.92 (1.38–2.66) |
| Previous cerclage* | |||
| • No | 1517 (97.6) | 656 (98.9) | Ref. |
| • Yes | 38 (2.4) | 7 (1.1) | 2.35 (1.02–5.40) |
| Previous preterm birth* | |||
| • No | 1008 (64.7) | 565 (84.8) | Ref. |
| • Yes | 550 (35.3) | 101 (15.2) | 3.05 (2.34–3.98) |
| Previous preterm labour* | |||
| • No | 1313 (84.5) | 604 (90.7) | Ref. |
| • Yes | 241 (15.5) | 62 (9.3) | 1.79 (1.28–2.50) |
| Previous pPROM* | |||
| • No | 1312 (84.4) | 599 (90.3) | Ref. |
| • Yes | 243 (15.6) | 64 (9.7) | 1.73 (1.16–2.59) |
| Previous newborn under 2500g* | |||
| • No | 1090 (71.0) | 571 (87.2) | Ref. |
| • Yes | 446 (29.0) | 84 (12.8) | 2.78 (2.12–3.65) |
| • Total | 2,682 (100) | 1,146 (100) |
OR*: Odds Ratio adjusted for the cluster effect design; CI: confidence interval; (*): excluded Primigravida from the analysis.
Values in bold mean they are statistically significant.