Effect of prenatal environmental tobacco smoke exposure on infant birth size

Background: There is increasing evidence that environmental tobacco smoke (ETS) exposure during pregnancy may adversely affect birth outcomes. Methods: From 2003 to 2006, a prospective study of 2972 nonsmoking Japanese pregnant women within Hokkaido Prefecture was conducted. Information about ETS exposure and birth outcomes were collected through self-administered questionnaires, biochemical analyses and hospital records. Results: Multiple linear regression models were used to find out the association of exposure to ETS during pregnancy with the birth outcomes. After adjusting for covariates, an inverse relationship between cotinine quartile groups and birth weight, birth length and birth head circumference was observed. However, stratification by infant gender revealed more reductions in birth weight (-66g, 95%CI: -124.2, -7.4; p = 0.027) and head circumference at the 4th cotinine quartile levels (-0.64cm, 95%CI: -1.163, -0.114; p = 0.017) among male infants. The effect of SHS exposure on birth length was more pronounced in female infants (-0.71cm, 95%CI: -1.310, -0.108; p = 0.021) at the highest cotinine level. Maternal tobacco smoke exposure through passive route affects birth size negatively, more especially the male infants suggesting a greater vulnerability of male conceptuses. Conclusion: The observed association confirms the health hazard that ETS exposure at home poses to pregnant women and their unborn babies. Both mothers and fathers should be the target of educational anti-tobacco campaigns and quit smoking programs to create smoke-free and healthy home environment.