Maternal smoking exposure during pregnancy is an established risk factor for childhood asthma, but the association between maternal pre-pregnancy smoking status and asthma risk is not well understood. This study examined the association between maternal smoking status before and during pregnancy and bronchial asthma at 3 years of age.
The data of 75,411 mother-child pairs, excluding the missing data of exposure and outcomes from the Japan Environment and Children's Study (JECS) were used. The association between prenatal maternal smoking status and the risk of bronchial asthma at 3 years of age was determined using multivariate logistic regression analysis.
The percentage of 3-year-old children with doctor-diagnosed bronchial asthma was 7.2%. The distribution of maternal smoking status before childbirth was as follows: Never = 60.0%, Quit before recognizing current pregnancy = 24.1%, Quit after finding out current pregnancy = 12.3%, and Still smoking = 3.6%. Maternal smoking during pregnancy was significantly associated with an increased risk of bronchial asthma at 3 years of age even after adjusting for pre- and postnatal covariates (adjusted odds ratio [aOR] 1.35, 95% confidence interval [CI] 1.16–1.57). Furthermore, mothers who quit before recognizing current pregnancy (aOR 1.10, 95% CI 1.02–1.18) or who quit after finding out about current pregnancy (aOR 1.11, 95% CI 1.01–1.23) were also significantly associated.
This study suggested that not only maternal smoking during pregnancy but also maternal smoking exposure of pre-pregnancy or early pregnancy may be associated with an increased risk of bronchial asthma in children.