The population attributable fraction for a decrease in average PM10 exposure during pregnancy to20 mg/m3 was 24% (95% CI: 10, 35%) for moderately preterm SGAnewborns and 13% (95% CI: 9, 16%) for term SGA newborns. The decrease in slope after the breakpoint was significant for the time windows entire pregnancy, two weeks after conception, and second trimester among term births, and the time windows entire pregnancy and last month among moderately preterm births. Es- timates for the significant breakpoints ranged from 27.2 to40.0 mg/m3.