Prenatal and Postnatal Risk Factors of Childhood Asthma

Background: Asthma affects 12% of Canadian children and the prevalence has shown a significant increase in recent years. This study aims to examine the association of prenatal and postnatal tobacco exposure with asthma throughout child development.

Methods: We examined data on Canadian children (aged 0-13 years) using the biennial survey, National Longitudinal Survey of Children and Youth (longitudinal sample: n=2,695; cross sectional sample: n=20,470) from 1994 to 2006. The likelihood of childhood asthma based on maternal characteristics (prenatal smoking, gestational diabetes, postnatal smoking), birth outcomes (type of delivery, gestational age and weight), breast feeding, parental asthma, ethnicity, child obesity, and environmental characteristics (postnatal exposure to smoking, socio economic status) were measured using multivariate logistic regression and longitudinal analysis. Mediating effects of breast feeding, obesity, type of delivery were closely examined.

Results: Preliminary analysis of infants (aged 0-1 years) from the 1998-1999 cross-sectional survey showed that of the 20% of infants exposed to prenatal smoking, 7% were diagnosed with asthma. Infant boys showed significantly higher prevalence of asthma compared to the girls (9% vs. 4%). Exposure to prenatal smoking varied across provinces from 12% (British Columbia) to 29% (Saskatewan). Among those who were exposed to prenatal smoking, breastfed infants showed significantly lower prevalence for asthma (20%) compared to non-breastfed infants (56%). Analyses from the longitudinal sample will present the influence of all other risk factors on asthma.

Discussion: This study highlights the change in risk factors for asthma throughout child development and captures the benefits of prospective studies on childhood asthma.