Maternal Second-Hand Smoke Exposure in Pregnancy Is Associated With Childhood Asthma Development

BACKGROUND: Childhood asthma development has been associated with active maternal smoking during pregnancy, but its association with maternal second-hand smoke exposure in pregnancy needs to be evaluated. OBJECTIVE: We investigated longitudinal associations between maternal smoke exposure in pregnancy and childhood asthma development. METHODS: In a population-based cohort of 5619 seven-year-old Toronto children, parents reported age of physician-diagnosed asthma development, maternal smoking during pregnancy, home second-hand smoke exposure from pregnancy until 7 years, demographics, and family history of atopy. By using Cox proportional and discrete-time hazard survival analyses, we evaluated associations between asthma and maternal smoking or home second-hand smoke exposure in pregnancy. RESULTS: During pregnancy, 5.0% of mothers smoked and 6.2% were nonsmokers and exposed to home second-hand smoke; 15.5% of children developed asthma. Children whose mothers smoked or were exposed to home second-hand smoke during pregnancy were more likely to develop asthma (adjusted hazard ratio [HR] 1.30 [95% CI, 1.06-1.60]). The association persisted for children of nonsmoking mothers with home second-hand smoke exposure during pregnancy (adjusted HR 1.34 [95% CI, 1.01-1.76]), children with asthma symptoms in the past year (adjusted HR 1.36 [95% CI, 1.03-1.79]), and after adjusting for home second-hand smoke exposure from birth to age 7 years. CONCLUSIONS: Maternal home second-hand smoke exposure during pregnancy is associated with incident physician-diagnosed childhood asthma, even if the mother does not smoke actively during pregnancy. Childhood asthma prevention programs should include smoking cessation strategies targeted toward smokers who live in the homes of smoking and nonsmoking pregnant women as well as pregnant women who smoke. (C) 2014 American Academy of Allergy, Asthma & Immunology