To the best of our knowledge, there is no epidemiological study on the association between gestational exposure to PM2.5 and congenital heart defects. In the current study, PM10 and PM2.5 were found to be correlated with the calculated mean value for gestational weeks 3–8 (r ¼ 0.54), and even more highly correlated when the half hourly raw data were used (r ¼ 0.89 regional average, without dust days r ¼ 0.60). This difference might be due to the fact that for PM10 more monitoring stations were available, thus reducing exposure misclassification (compared to PM2.5). The fact that different associations between the particulate fractions and the health outcomes were observed might be due to the different sources of fine and coarse particles in the Tel-Aviv region (Freiman et al., 2006).