Discussion
For infants born after 31 weeks of gestation, we observed sig- nificant associations between in utero PM10 exposure and birthweight as well as SGA. The effects of maternal PM10 exposure on both outcomes were considerably higher for moderately preterm neonates (32–36 weeks) than for those born at term. Susceptibility to air pollution was found to be higher for multiparous women and for lower maternal age and parental education. For both birth weight and SGA, the estimated breakpoint and the significance of the change in slope depended on the studied time window. In general, significant breakpoints were estimated to lie around35 mg/m3 and the estimated decrease in birth weight was largesfor PM10 concentrations below this level. Twenty seven percent of our study population had an average pregnancy exposure above35 mg/m3.