95. Critical Time Windows for Air Pollution Exposure and Birth Weight in a Multicity Canadian Pregnancy Cohort (lay summary)

Johnson M,  Shin HH, Roberts E, Sun L, Fisher M, Hystad P, Van Donkelaar A, Martin RV, Fraser WD, Lavigne E, Clark N, Beaulac V, Arbuckle TE. Epidemiology 2022 Jan 1;33(1):7-16. doi: 10.1097/EDE.0000000000001428

Exposure to air pollution during pregnancy has been associated with low birth weight and other adverse birth outcomes, but time windows within pregnancy when air pollution may be more harmful are still unknown.  Previous research comparing associations between trimesters has reported inconsistent results.  Our goal was to identify critical periods during pregnancy using a flexible selection method, which allowed us to examine any time window during pregnancy, rather than just the fixed trimesters.

We used a sophisticated statistical approach to examine the impacts of exposure to fine particulate matter (PM2.5) and nitrogen dioxide (NO2) on birth weight among 1300 live singleton babies from the MIREC Study. We identified critical periods for both PM2.5 and NO2 in mid- and late-pregnancy, when exposure to air pollution was more highly associated with birth weight (5 g reduction in birth weight per 1 ug/m3 PM2.5, and 3 g per 1 ppb NO2).  The critical periods varied in duration, and straddled or fell within the trimesters; suggesting that air pollution impacts on fetal development may not be adequately captured by traditional trimester-based analyses.

This research was led by scientists at Health Canada.