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Associations between second-hand smoke exposure in pregnancy and age of childhood asthma development


Maternal smoking during pregnancy has been associated with an increased hazard of incident childhood asthma. We investigated the association between any second-hand smoke exposure in early life and childhood asthma development.


In the Toronto Child Health Evaluation Questionnaire, parents of 5619 grades 1-2 students reported age of physician-diagnosed asthma development, exposure to maternal and household second-hand smoke during pregnancy and the first year of life, socio-demographic factors, and other early-life exposures such as mold and cockroach. Using Cox proportional hazard models, we evaluated the longitudinal associations between second-hand smoke exposure and age of asthma development.


Household second-hand smoke exposure prevalence was 8.3% during pregnancy and 10.6% in the first year of life; 15.5% of children developed asthma. After adjusting for sex, prematurity, being born in Canada and maternal asthma, children exposed to home second-hand smoke during pregnancy were more likely to develop asthma and developed asthma sooner [adjusted hazard ratio (HR) 1.36, 95% confidence interval (CI): 1.09, 1.70], even after excluding children whose mothers smoked in pregnancy (HR 1.53, 95% CI: 1.09, 2.14). The association strengthened (HR 1.88, 95% CI: 1.16, 3.02) after adjusting for home second-hand smoke exposure in the first year.


Home second-hand smoke exposure during pregnancy is associated with an increased hazard of childhood asthma development, even if the mother is not a smoker. Recommendations for smoking cessation during pregnancy should focus on pregnant women and members of their households.

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Correspondence to Elinor Simons.

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This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Simons, E., To, T., Moineddin, R. et al. Associations between second-hand smoke exposure in pregnancy and age of childhood asthma development. All Asth Clin Immun 8 (Suppl 1), A4 (2012).

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  • Asthma
  • Smoking Cessation
  • Childhood Asthma
  • Maternal Smoking
  • Adjust Hazard Ratio