PURPOSE OF THE STUDY.
The goal of this study was to determine longitudinal associations between maternal secondhand smoke exposure during pregnancy and the development of childhood asthma.
This population-based cohort included 5619 seven-year-old children in grades 1 and 2 recruited from a random sample of 283 public schools in the greater Toronto area.
Cross-sectional data were collected on demographic characteristics, family history of atopy, smoke exposure, and outcome information until age 6 or 7 years by using validated questionnaires completed by a parent or guardian for all 5619 children. Further detailed longitudinal exposure data were obtained via telephone survey on a randomly selected case-control subset of 1497 children, one-half of whom had a reported history of asthma or wheezing. Statistical methods used to analyze associations included Cox proportional and discrete-time hazard survival analyses.
Increased risk of asthma development was associated with maternal smoking or home secondhand smoke exposure during pregnancy and first year of life, male gender, preterm birth, and maternal asthma. Breastfeeding at least 6 months conferred a protective effect. When adjusting for the aforementioned factors, maternal smoking or secondhand smoke exposure during pregnancy was associated with a 30% increase in adjusted hazard of childhood asthma development. This association persisted for secondhand smoke exposure alone during pregnancy as well as after adjusting for secondhand smoke exposure during the first year of life and for exposure from birth to 7 years.
The results of this study suggest that there is an increased risk of developing childhood asthma with maternal secondhand smoke exposure during pregnancy, regardless of the mother’s active smoking status during that time.
This study is the first to evaluate the association between maternal secondhand smoke exposure during pregnancy and childhood asthma development. Previous studies evaluated maternal smoking status during pregnancy, and others assessed early-life exposures after birth. Such findings highlight the need for smoking cessation education not only for pregnant mothers but for all smokers in the home.
- Copyright © 2014 by the American Academy of Pediatrics