HRs (95% CI) of preterm (26–36 gestational weeks) and early-term births (37–38 gestational weeks) for a 10% increase in the proportion of pregnancy time under smoking ban for the combined and single susceptibility periods
| Preterm birth | Early-term birth | |
|---|---|---|
| Gestational period | HR (95% CI) | HR (95% CI) |
| Whole pregnancy | 0.991 (0.984 to 0.997) | 0.997 (0.994 to 1.000) |
| 2nd and 3rd trimesters | 0.992 (0.985 to 0.998) | 0.997 (0.994 to 1.000) |
| 3rd trimester | 0.995 (0.990 to 1.000) | 0.996 (0.994 to 0.998) |
| 2nd trimester | 0.991 (0.984 to 0.997) | 0.999 (0.996 to 1.002) |
| 1st trimester | 0.992 (0.986 to 0.997) | 0.999 (0.996 to 1.002) |
Proportion in first and second trimester: the number of days the pregnancy was under the smoking ban divided by the total duration of respective trimester. For the third trimester: proportion of days between the start of the third trimester and the end of the preceding week. Duration indicators were included separately in models to explore susceptibility windows of exposure.