Table 4.
Relative risk of preterm birth by risk group in women with treatment before birth
| Risk group (largest category for volume or depth) | No (%) cases | No (%) controls | Relative risk* (95% CI) |
|---|---|---|---|
| Small depth AND volume (<10 mm and ≤1.77 cm3) | 142 (25.4) | 192 (34.5) | 1 (reference) |
| Medium depth OR volume (10-14 mm or 1.78-2.65 cm3) | 144 (25.8) | 170 (30.6) | 1.15 (0.85 to 1.55) |
| Large depth OR volume (15-20 mm or ≥2.66 cm3) | 149 (26.7) | 95 (17.1) | 1.97 (1.43 to 2.72) |
| Very large depth (≥20 mm) | 54 (9.7) | 28 (5.0) | 2.44 (1.52 to 3.93) |
| Unknown depth AND volume | 69 (12.4) | 71 (12.8) | 1.30 (0.89 to 1.91) |
*Adjusted for parity, index of multiple deprivation, maternal age at delivery, and study site.