Invited Commentary: Ambient Environment and the Risk of Preterm Birth.

Preterm birth is a common adverse birth outcome known to be associated with increased infant mortality, and it often results in a higher burden of offspring morbidity in both the short and long terms. The potential for environmental factors, particularly air pollution and meteorological parameters, to increase preterm birth risk has received significant attention worldwide, but the findings are generally inconsistent, with variations in study designs and methods across populations and geographic locations. In the current issue of the Journal, Giorgis-Allemand et al. (Am J Epidemiol. 2017;185(4):247-258) take the field a step further than most prior investigations of the ambient environment. They examined the associations of ambient air pollution and meteorological factors with preterm risk among 13 cohorts across 11 European countries. No association with air pollution was observed, but associations with increased preterm birth risk were found for both increased atmospheric pressure and ambient temperature exposures during the first trimester. The study is notable in attempting to address several important issues that challenge the field, including exposure misclassification and defining critical windows of exposure. Their comprehensive evaluation of ambient exposures is to be commended.