Jung CR, et al. - Researchers evaluated how weekly average fine particulate matter (particulate matter with an aerodynamic diameter less than 2.5 μm [PM_2.5]) exposure during pregnancy and infancy affects asthma, as well as vulnerable times for exposure to help explain possible mechanisms of the effects of PM_2.5 on asthma symptoms. From the Taiwan Maternal and Child Health Database, they assessed data from a birth cohort of 184,604 children born during 2004-2011 in Taichung City and followed the cohort until 2014. To estimate PM_2.5 exposure for each subject, they applied a daily satellite-based hybrid model. Outcomes revealed an association of both prenatal and postnatal exposures to PM_2.5 with later development of asthma. Early gestation and midgestation and infancy were identified as possible vulnerable time windows.