Maternal smoking in pregnancy, fetal development, and childhood asthma

Objectives. We examined the relationships among maternal smoking in pregnancy, fetal development, and the risk of asthma in childhood. Methods. We conducted a population-based cohort study, where all 58841 singleton births were followed for 7 years using nationwide registries. Results. Maternal smoking increased the risk of asthma (adjusted odds ratio = 1.35; 95% confidence interval = 1.13, 1.62 for high exposure). Low birthweight and preterm delivery increased the risk of asthma at the age of 7, whereas being small for gestational age did not. Conclusions. Maternal smoking in pregnancy increases the risk of asthma during the first 7 years of life, and only a small fraction of the effect seems to be mediated through fetal growth. (Am J Public Health. 2004;94:136-140).