Investigating the acute effects of fine particulate matter on stillbirth risk in Ulaanbaatar, Mongolia

Abstract

Investigating the acute effects of fine particulate matter on stillbirth risk in Ulaanbaatar, MongoliaTemuulen Enebish, Rima Habre, Carrie V. Breton, Nomindelger Tuvshindorj, Gantuya Tumur, David Warburton, Meredith FranklinBackground: Ulaanbaatar city (UB), the capital and the home to half of Mongolia’s total population, has experienced extreme seasonal air pollution in the past two decades with fine particulate matter (PM2.5) levels reaching 500 µg/m3. We investigated whether short-term increase in daily PM2.5 shortly before delivery results in stillbirth in UB between 2010 and 2018.Methods: We collected individual level data on 1570 stillbirths from hospital records (2010-2013) and surveillance database (2014-2018). Ambient air pollution exposure was estimated at residential area of each case using a Random Forest model. We utilized time-stratified case-crossover design to estimate the relative odds of stillbirth per interquartile range (IQR) increase in PM2.5 for different exposure windows of individual and cumulative lags of 2-6 days before delivery. Effect estimates were derived from a conditional logistic regression model and individual level characteristics were analyzed for effect modification.Results: We observed significantly elevated relative odds of stillbirth per IQR increase in PM2.5 3 days (odds ratio [OR]=1.50, 95% confidence interval [CI]=1.06-2.12) and 6 days (OR=1.41, 95% CI=1.00-1.99) before delivery after adjusting for temperature (spline) and PM10. These estimates increased (lag day 3: OR=1.93, 95% CI=1.25-2.98, lag day 6: OR=1.73, 95% CI=1.11-2.68) after restricting the analysis to cold season (Oct-Mar). We saw elevated yet not significant effect estimates for cumulative lag day averages of 2-3 and 2-6 days. When only looking at stillbirths in cold season, relative odds of stillbirth for all lag day averages increased with odds ratio for 2-3 lag day averages reaching 2.03 (95% CI=1.20-3.44).Conclusion: Acute exposure to PM2.5 before delivery may trigger stillbirth.