To evaluate the association between increased exposure to airborne fine particulate matter (PM_2.5) during the periconception period with risk of congenital anomalies.

Using birth certificate data from the Ohio Department of Health (2006-2010) and PM_2.5 data from the US Environmental Protection Agency's 57 monitoring stations located throughout Ohio, the geographic coordinates of the mother's residence for each birth were linked to the nearest PM_2.5 monitoring station and monthly exposure averages were calculated. The association between congenital anomalies and increased PM_2.5 levels was estimated, with adjustment for coexistent risk factors.

After adjustment for coexisting risk factors, exposure to increased levels of PM_2.5 in the air during the periconception period was modestly associated with risk of congenital anomalies. Compared with other periconception exposure windows, increased exposure during the 1 month before conception was associated with the highest risk increase at lesser distances from monitoring stations. The strongest influences of PM_2.5 on individual malformations were found with abdominal wall defects and hypospadias, especially during the 1-month preconception.

Increased exposure to PM_2.5 in the periconception period is associated with some modest risk increases for congenital malformations. The most susceptible time of exposure appears to be the 1 month before and after conception. Although the increased risk with PM_2.5 exposure is modest, the potential impact on a population basis is noteworthy because all pregnant women have some degree of exposure.