A systematic review and meta-analysis of prospective studies on the association between maternal cigarette smoking and preterm delivery

We have attempted to quantify the most up-to-date estimate of the associati on between cigarette smoking by the mother and preterm delivery. Studies we re selected for inclusion in this review if they were prospective, reported data stratified across at least two levels of maternal smoking, and define d preterm delivery on the basis of gestational age. In a meta-analysis we c ombined results from multiple studies that reported on preterm delivery and maternal smoking during pregnancy. Pooled odds ratios were computed for va rious strata of smoking intensity with the Mantel-Haenszel fixed-effects mo del. Twenty studies met all inclusion criteria and were included in meta-an alysis. The pooled point estimate from 20 prospective studies on any matern al smoking versus no maternal smoking was 1.27 (95% confidence interval, 1. 21-1.33). Subgroup analyses stratifying maternal smoking on number of cigar ettes per day suggest a dose-response relationship at low to moderate level s of smoking, which was not further increased at high levels of smoking. A nonsignificant level of publication bias appears to exist in the smoking-pr eterm delivery literature. Cigarette smoking is a preventable risk factor t hat is associated with preterm delivery. Consistent results across many stu dy populations and research designs and evidence of a dose-response relatio nship support its causal role in preterm delivery.