71 - Antenatal wildfire smoke exposure and hypertensive disorders of pregnancy

Objective: Prior evidence demonstrates an association between wildfire smoke exposure and preterm birth (PTB). We aimed to assess wildfire smoke exposure and spontaneous and medically indicated PTB and potential drivers of this association. Specifically, we sought to examine wildfire smoke exposure with hypertensive disorders of pregnancy (HDP), a leading contributor to medically indicated preterm birth.

Study Design: Birth certificate and delivery hospitalization data among singleton livebirths in California from 2007-2012 were combined with daily zip code level estimates of wildfire smoke intensity derived from satellite-based estimates of wildfire smoke plume boundaries and high-resolution gridded estimates of surface particulate matter, PM2.5 (a standard measure of inhalable particulate pollution), concentrations. The exposure period was 4 weeks preconception through gestational week 20. Logistic regression models were used to assess associations between the number of wildfire smoke exposed days and PTB phenotypes and HDP. For each outcome, wildfire smoke was modelled based on the period and intensity of exposure. Exposure to wildfire smoke of any intensity, and by low, moderate, and high levels were analyzed by the total exposure period, as well as categorized by the preconception period, 1st trimester, and weeks 14-20 gestational age.

Results: Our analysis included 2,548,347 pregnant individuals, of which 86% were exposed to at least 1 day of wildfire smoke during the exposure period, with an average of 7.5 days of wildfire smoke exposure. Despite analytically investigating distinct exposure windows and smoke intensities, we did not observe an association with HDP. Wildfire smoke was significantly (p < 0.0001) associated with spontaneous preterm birth, such that each additional day of smoke exposure conferred 0.3% increased odds of delivering < 37 weeks spontaneously.

Conclusion: Our study found the association of wildfire smoke exposure with PTB was driven by spontaneous PTB rather than an increased risk of hypertensive disorders of pregnancy or medically indicated PTB.