Association between fine particulate matter (PM2.5) and infant mortality in a North Carolina Birth Cohort (2003-2015)
Background: While the association between fine particulate matter (PM2.5) and adult mortality is well-established, few studies have examined the association between long-term PM2.5 exposure and infant mortality.
Methods: We conducted an unmatched case-control study of 5,992 infant mortality cases and 60,000 randomly selected controls from a North Carolina Birth Cohort (2003-2015). PM2.5 during critical exposure periods (trimesters, pregnancy, first month alive) were estimated using residential address and a national spatiotemporal model at census block centroid. We fit adjusted logistic regression models and calculated odds ratios (ORs) and 95% confidence intervals (CIs). Due to differences in PM2.5 over time, we stratified analyses into two periods: 2003-2009 (mean=12.1 µg/m3, IQR:10.8-13.5) and 2011-2015 (mean=8.4 µg/m3, IQR:7.7-9.0). We assessed effect measure modification by birthing parent race/ethnicity, gestational age and PM2.5 concentrations.
Results: For births 2003-2015, the odds of infant mortality increased by 12% (95%CI: 1.06, 1.17) per 4.0 µg/m3 increase in PM2.5 exposure averaged over the pregnancy. After stratifying, we observed an increase of 4% (95%CI: 0.95, 1.14) for births in 2003-2009 and decrease of 15% (95%CI: 0.72, 1.01) for births in 2011-2015. Among infants with higher PM2.5 exposure (≥ 12 µg/m3) during pregnancy, the odds of infant mortality increased (OR:2.69; 95%CI: 2.17, 3.34) whereas the lower exposure (<8 µg/m3) group reported decreased odds (OR:0.50; 95%CI: 0.28, 0.89).
Conclusions: We observed differing associations of PM2.5 exposure with infant mortality across higher versus lower PM2.5 concentrations. These findings suggest the importance of accounting for long-term trends of decreasing PM2.5 concentrations in future research.