Objective: To evaluate a possible dose-response relationship between active maternal smoking during pregnancy and adverse perinatal outcome.
Design: Retrospective cohort study.
Setting: Population-based in Montreal, Quebec, Canada.
Population: Women who gave birth to a liveborn or stillborn infant during the period of January 2001 to December 2007.
Methods: Active smokers of different daily cigarette consumption (n=1646) were identified through maternal self-reporting. The reference group comprised 19,292 non-smoking women who delivered during the same period.
Main outcome measures: Birth weight, preterm delivery rate, fetal and neonatal mortality and morbidity, and congenital malformations.
Results: Preterm delivery rate was significantly higher in the smoking group compared with controls (22.2% vs. 12.4%, P<0.05), as was intrauterine fetal demise (1.4% vs. 0.3%, P<0.05). Newborns of active smokers were more likely to weigh less (3150±759 g vs. 3377±604 g, P<0.05), suffer from respiratory distress syndrome (2.5% vs. 1.3%, P<0.05), suffer from a cardiac malformation (1.5% vs. 0.8%, P<0.05), and die (neonatal death 1.2% vs. 0.6%, P<0.05). A dose-response relationship was demonstrated between levels of daily cigarette smoking and several adverse outcomes. Using multiple regression models, smoking was found to be an independent predictor of preterm delivery (odds ratios (OR) 1.9, 95% confidence intervals (95%CI) 1.6-2), and intrauterine fetal demise (OR 2.4, 95%CI 1.4-4.2).
Conclusion: Any amount of daily smoking appears to harm the fetus and newborn. As pregnancy may be a "window of opportunity" for behavioural changes, efforts to promote smoking cessation should be encouraged.