Effects of prenatal exposure to air particulate matter on the risk of preterm birth and roles of maternal and cord blood LINE-1 methylation: A birth cohort study in Guangzhou, China.

•Preterm birth (PTB) risk was positively associated with prenatal exposure to PM2.5 and PM1, and a slightly greater effect was found for PM1 compared with PM2.5.•Gestational weeks 12 to 20 might be the critical window with the peak effect in the 16th week.•Fetal LINE-1 methylation was simultaneously associated with prenatal exposure to ambient particulate air pollution (PM) and PTB risk, indicating that LINE-1 methylation alternation might be an underlying mechanism of PM increasing PTB risk. However, the roles of maternal LINE-1 methylation may differ compared with their infants.