Fetal and infant death associated with short-term ozone exposure

Abstract

Background: Air pollution is linked to adverse pregnancy outcomes such as preterm births, but few studies evaluated its acute impact on fetal and infant mortality. We evaluated short-term impacts of warm-season ozone and cold-season fine particulate matter <2.5 microns (PM2.5) exposures on the risk of fetal death (>20 weeks) and infant mortality (live birth to one year). Methods: This time-stratified case-crossover analysis includes 1,880 singleton fetal deaths (2007-2011) and 3,229 singleton infant deaths (2007-2015) from the San Joaquin Valley (SJV), California. Daily ozone and PM2.5 were estimated by the SJV Air Pollution Control District and geospatially linked to maternal zip code at birth. Critical exposure windows of interest included the day of death (lag 0) up to 14 days before (lag 14). Conditional logistic regression models estimated the odds ratio (OR) and 95% confidence intervals (CI) for each 5 units increase in pollutant. Results: In warm season (May-October), a 5-ppb increase in ozone was associated with a 7% (95% CI: 2%-13%) increased risk of fetal death and 6% (95% CI: 2%-10%) increased risk of infant death within two weeks. The estimates were generally consistent from lag 0 to lag 14 for both mortality outcomes, with evidence of slightly stronger estimates for fetal death compared to infant death during certain lags. During lag 7, a 5-ppb increase in ozone was associated with a 9% increased risk in fetal death (95% CI: 5%-14%) and a 4% (95% CI: 1%-7%) increased risk in infant death. No associations were observed for cold-season PM2.5. Conclusions: Ozone exposure is positively associated with short-term risk of fetal and infant mortality in the warm season. Given the ubiquitous nature of air pollution, these associations merit further investigation. Meanwhile, efforts to minimize exposures among pregnant women may be warranted. Keywords: pollution, infant mortality, fetal death, stillbirth, pregnancy, mortality, ozone