A time-to-event analysis of the association between ambient air pollution and risk of spontaneous abortion using vital records in the U.S. state of Georgia (2005-2014).

We examined the association between ambient air pollution exposure and risk of spontaneous abortion (SAB) using Georgia state-wide fetal death records from 2005-2014. Each SAB case was matched to four non-SAB pregnancies by maternal residential county and conception month. Daily concentrations of ten pollutants were estimated and linked to maternal residential census tracts. Cox regression was used to estimate hazard ratios (HR) across four prenatal exposure windows (first month, weekly, cumulative weekly average over the first trimester, cumulative weekly average over the second trimester). Our dataset contained 47,649 SABs with a median gestational age of nine weeks. Carbon monoxide (CO) showed the strongest association, with an HR of 1.12 (1.05, 1.20) per 0.43 ppm increase in average first month exposure, and 1.06 (1.02, 1.10) per 0.42 ppm increase in average weekly exposure. Nitrogen dioxide (NO2) also exhibited elevated HRs. Other pollutants like nitrate compounds (NO3), nitrogen oxides (NOx), and organic carbon (OC) showed positive associations, while ozone (O3), PM2.5, PM10, elemental carbon (EC), and ammonium ions (NH4) were null. Early pregnancy exposure to traffic-related pollutants may increase SAB risk, highlighting potential benefits of air pollution regulation.