Prenatal exposure to particulate matter and infant birth outcomes: Evidence from a population-wide database

There are growing concerns about the impact of pollution on maternal and infant health. Despite an extensive correlational literature, however, observational studies which adopt methods that seek to address potential biases due to unmeasured confounders draw mixed conclusions. Using a population database of births in Northern Ireland linked to localised geographic information on pollution in mothers’ postcodes (zipcodes) of residence during pregnancy, we examine whether prenatal exposure to PM2.5 is associated with a comprehensive range of birth outcomes, including placental health. Overall, we find little evidence that particulate matter is related to infant outcomes, at the pollution levels experienced in Northern Ireland, once we implement a mother fixed effects approach that accounts for birth-invariant factors common to mothers. This contrasts with clear unconditional and conditional associations when the data are pooled. While reducing ambient air pollution remains an urgent public health priority globally, our results imply that further improvements in short-run levels of prenatal PM2.5 exposure in a relatively low-pollution, developed country context, are unlikely to impact on birth outcomes at the population level.