3.2. Air pollution and associations with congenital heart defects
The crude and adjusted ORs (95% CI) to all pollutants are presented in Tables 3 and 4, respectively. Most of the difference between the crude and adjusted models could be attributed to the addition of the season of conception as well as the covariates of year of birth and religion. In general, we found insignificant associations between air pollution and congenital heart defects. However two exceptions were found for particulate matter. For continuous exposure to PM10 (10 μg/m3 increase) the adjusted OR for multiple congenital heart defect cases was 1.05 (95% CI: 1.01 to 1.10). For continuous exposure to PM2.5 (5 μg/m3 increase), the adjusted OR for patent ductus arteriosus cases was 0.78 (95% CI: 0.68 to 0.91). For the gaseous pollutants, CO, O3, NO2 and SO2, there was no association between maternal exposure during pregnancy and risks of isolated patent ductus arteriosus, ventricular septal defect and atrial and atrial septal defects or multiple congenital heart defect cases.