Table 3.
The odds of all preterm births (20- < 37 weeks gestation) and third trimester preterm births (28- < 37 weeks gestation) across maternal smoking status categories
| Preterm 20- < 37 weeks | ||||
| Smoking Status | Crude OR | 95% CI | Adjusted ORa | 95% CI |
| No trimester smokers | 0.85 | 0.82, 0.89* | 0.90 | 0.86, 0.94* |
| 1st trimester only, low (ref.) | 1 | 1 | 1 | 1 |
| 1st trimester only, high | 0.97 | 0.87, 1.08 | 0.98 | 0.88, 1.09 |
| 1st & 2nd trimesters, low | 1.53 | 1.43, 1.64* | 1.51 | 1.41, 1.61* |
| 1st & 2nd trimesters, high | 1.86 | 1.67, 2.07* | 1.85 | 1.66, 2.06* |
| 2nd & 3rd trimesters, low | 0.98 | 0.89, 1.08 | 0.95 | 0.86, 1.05 |
| 2nd & 3rd trimesters, high | 1.06 | 0.80, 1.41 | 1.03 | 0.77, 1.36 |
| All 3 trimesters, low | 1.21 | 1.16, 1.26* | 1.20 | 1.14, 1.25* |
| All 3 trimesters, high | 1.31 | 1.25, 1.38* | 1.33 | 1.26, 1.40* |
| Preterm 28- < 37 weeks | ||||
| Smoking Status | Crude OR | 95% CI | Adjusted ORa | 95% CI |
| No trimester smokers | 0.88 | 0.84, 0.92* | 0.93 | 0.89, 0.97* |
| 1st trimester only, low (ref.) | 1 | 1 | 1 | 1 |
| 1st trimester only, high | 0.96 | 0.86, 1.08 | 0.97 | 0.86, 1.08 |
| 1st & 2nd trimesters, low | 1.34 | 1.24, 1.44* | 1.32 | 1.22, 1.42* |
| 1st & 2nd trimesters, high | 1.62 | 1.44, 1.83* | 1.61 | 1.43, 1.82* |
| 2nd & 3rd trimesters, low | 1.03 | 0.93, 1.14 | 1.00 | 0.90, 1.11 |
| 2nd & 3rd trimesters, high | 1.09 | 0.81, 1.46 | 1.05 | 0.79, 1.40 |
| All 3 trimesters, low | 1.27 | 1.21, 1.33* | 1.25 | 1.20, 1.31* |
| All 3 trimesters, high | 1.39 | 1.32, 1.47* | 1.40 | 1.33, 1.48* |
aAnalyses were adjusted for: maternal race/ethnicity, age, education, and marital status; low intensity: 1–19 cigarettes/day; high intensity: ≥ 20 cigarettes/day; *p < 0.05; CI-confidence interval