Table IIB.
Prospective studies on smoking and preterm delivery by level of smoking: Heavy smoking during pregnancy
| Series | Year | Exposure criteria | Unexposed criteria | Exposed (PTD/total) | Unexposed (PTD/total) | Odds ratio | 95% Confidence interval |
|---|---|---|---|---|---|---|---|
| Ahlborg and Bodin8 | 1991 | Active; ≥20 cigarettes/d | No exposure | 11/132 | 86/2281 | 2.32 | 1.21-4.46 |
| Doucette and Bracken11 | 1993 | ≥21 cigarettes/d in month | 0 cigarettes/d in month 2 | 7/92 | 122/2630 | 1.69 | 0.77-3.74 |
| Kramer et al14 | 1992 | ≥11 cigarettes/d | 0 cigarettes/d on average during pregnancy | — | — | 1.27 | 1.08-1.50 |
| Nordentoft et al16 | 1996 | ≥16 cigarettes/d at 20 wk | Nonsmoker at 20 wk | — | — | 0.95 | 0.41-2.23 |
| Peacock et al18 | 1995 | ≥15 cigarettes/d at booking, 28th wk | Nonsmoker | 7/120 | 26/309 | 0.67 | 0.28-1.60 |
| Shiono et al21 | 1986 | ≥1 pack/d during pregnancy | None during pregnancy | — | — | 1.20 | 1.10-1.40 |
| van den Berg and Oechsli25 | 1977 | ≥15 cigarettes/d | Never smoked | 152/2077 | 195/4249 | 1.64 | 1.32-2.04 |
| Wisborg et al27 | 1996 | ≥11 cigarettes/d at 16 wk | Nonsmoker | 16/193 | 86/2339 | 2.37 | 1.36-4.13 |
| Yerushalmy28 | 1964 | ≥21 cigarettes/d at interview | None during pregnancy | 25/267 | 223/3010 | 1.29 | 0.84-1.99 |
| Combined* | — | — | — | — | — | 1.31 | 1.20-1.42 |
PTD, Preterm delivery.
*
Mantel-Haenszel fixed-effects model.