Table 1. The associations between maternal covariates and preterm birth.
| Spontaneous #cases = 1756, #controls = 57267 | Induced #cases = 895, #controls = 57267 | |||
| OR (CI 0.95) | P-value | OR (CI 0.95) | P-value | |
| Civil status (coupled/married compared to single) | 0.98 (0.69–1.39) | 0.9 | 0.97 (0.60–1.57) | 0.9 |
| Height (per 10 cm) | 0.76 (0.70–0.83) | <10−9 | 0.89 (0.79–0.99) | 0.04 |
| Nonsmoker | 1 | 0.19 | 1 | 0.002 |
| Occasionally smoker | 0.87 (0.75–1.02) | 0.97 (0.79–1.21) | ||
| ≥15 cigarettes/day | 1.01 (0.86–1.18) | 1.42 (1.17–1.73) | ||
| High level proficiencies | 1 | 0.015 | 1 | 0.32 |
| Medium level proficiencies | 1.12 (0.91–1.37) | 1.03 (0.78–1.36) | ||
| Skilled | 1.13 (0.91–1.40) | 1.01 (0.75–1.35) | ||
| Students | 1.12 (0.89–1.41) | 0.90 (0.65–1.25) | ||
| Unskilled | 1.25 (1.01–1.54) | 1.06 (0.79–1.42) | ||
| Unemployed | 1.47 (1.16–1.87) | 1.28 (0.93–1.76) | ||
| Age≤20 | 1 | 0.13 | 1 | <0.001 |
| 21≤Age≤39 | 1.45 (0.86–2.44) | 2.55 (0.94–6.89) | ||
| Age≥40 | 2.12 (1.03–4.39) | 6.24 (2.05–19.05) | ||
| BMI≤18.5 | 1 | <0.001 | 1 | 0.09 |
| 18.6≤BMI≤24.9 | 0.75 (0.60–0.93) | 0.88 (0.63–1.23) | ||
| 25.0≤BMI≤29.9 | 0.65 (0.51–0.83) | 1.04 (0.73–1.48) | ||
| 30.0≤BMI≤34.9 | 0.93 (0.70–1.23) | 1.11 (0.73–1.68) | ||
| BMI≥35.0 | 0.96 (0.66–1.39) | 1.37 (0.83–2.28) | ||
| Nulliparous | 1 | <10−10 | 1 | <10−7 |
| Primiparous | 0.48 (0.42–0.54) | 0.63 (0.54–0.75) | ||
| Multiparous | 0.40 (0.34–0.49) | 0.70 (0.56–0.87) | ||
The marginal effect on preterm birth is calculated by a multivariate model with confounders/covariates and quintilized pattern scores for Western-type diet as predictor. Results are from stratification of the cases into spontaneous and induced births respectively.