Prenatal exposure to wildfire PM2.5 and pregnancy loss in Colorado, USA, 2007–2018

BACKGROUND: The association between wildfire smoke (WFS) exposure and pregnancy loss has been understudied. Here, we examined the association between prenatal wildfire-specific particulate matter ≤2.5 µm (PM2.5) exposure and pregnancy loss in Colorado, USA. METHODS: We retrieved all birth records from the 17 'Front Range' counties (just east of the Rocky Mountains) of Colorado from 2007 to 2018 (n = 614 321). We considered two PM2.5 exposures-wildfire-specific PM2.5 from a novel machine learning model and non-wildfire PM2.5 constructed using the Community Multiscale Air Quality model. We fitted quasi-Poisson distributed lag models to estimate the associations between the two weekly-resolved PM2.5 exposures during pregnancy and live birth-identified conceptions (LBICs) in each county. That is, we used the predicted change in the LBICs to directly infer the change in the number of pregnancy losses due to the exposure. RESULTS: Average weekly non-wildfire PM2.5 was 6.2 µg/m3 (SD 2.3). In weeks with non-zero WFS (27% of all county-weeks), the average wildfire-specific PM2.5 was 0.92 µg/m3 (SD: 1.55). Wildfire-specific PM2.5 appeared important in gestational weeks 6-13-a 1-µg/m3 higher exposure sustained in these gestational weeks was associated with 20 [95% confidence interval (CI): 4-34] losses/year. In contrast, the cumulative association with non-wildfire PM2.5 was stronger-a 1-µg/m3 higher exposure sustained in every week of pregnancy was associated with 84 (95% CI: 46-129) losses/year. CONCLUSION: Our findings suggest that both wildfire-specific and non-wildfire PM2.5 exposures were associated with more pregnancy loss and add to the growing literature on the harmful effects of wildfires and, more broadly, air pollution.