Impact of Scotland's Smoke-Free Legislation on Pregnancy Complications: Retrospective Cohort Study

Background: Both active smoking and environmental tobacco smoke exposure are associated with pregnancy complications. In March 2006, Scotland implemented legislation prohibiting smoking in all wholly or partially enclosed public spaces. The aim of this study was to determine the impact of this legislation on preterm delivery and small for gestational age. Methods and Findings: We conducted logistic regression analyses using national administrative pregnancy data covering the whole of Scotland. Of the two breakpoints tested, 1 January 2006 produced a better fit than the date when the legislation came into force (26 March 2006), suggesting an anticipatory effect. Among the 716,941 eligible women who conceived between August 1995 and February 2009 and subsequently delivered a live-born, singleton infant between 24 and 44 wk gestation, the prevalence of current smoking fell from 25.4% before legislation to 18.8% after legislation (p<0.001). Three months prior to the legislation, there were significant decreases in small for gestational age (-4.52%, 95% CI -8.28, -0.60, p = 0.024), overall preterm delivery (-11.72%, 95% CI -15.87, -7.35, p<0.001), and spontaneous preterm labour (-11.35%, 95% CI -17.20, -5.09, p = 0.001). In sub-group analyses, significant reductions were observed among both current and never smokers. Conclusions: Reductions were observed in the risk of preterm delivery and small for gestational age 3 mo prior to the introduction of legislation, although the former reversed partially following the legislation. There is growing evidence of the potential for tobacco control legislation to have a positive impact on health.