BACKGROUND AND AIM: In-utero exposure to particulate matter with aerodynamic diameter less than 2.5µm (PM2.5) in the 3rd trimester has been linked with low birth weight and childhood obesity risk, especially in Hispanic populations. However, previous results have been mixed, likely due to measurement error introduced by estimating personal exposure from ambient data. We investigated the effect of total personal PM2.5 exposure on birthweight and whether it differed by indoor vs outdoor origin in the MADRES cohort study. METHODS: Personal PM2.5 exposure was measured in 206 pregnant women in the 3rd trimester using 48-hour integrated, filter-based sampling. Linear regression was used to test the association between personal PM2.5 exposure and birthweight, adjusting for gestational age, parity, race, maternal age, diabetes, and smoking. Interactions of PM2.5 with indoor sources, home ventilation or time spent indoors tested whether the effect of total PM2.5 on birthweight varied by predominant origin of PM2.5. RESULTS:Participants were predominately Hispanic (79.8%) with mean (SD) gestational age of 39.0 (1.5) weeks, age of 28.2 (6.0) years, and pre-pregnancy BMI of 28.8 (6.8) kg/m2. Mean 48 hour 3rd trimester PM2.5 exposure was 24.5 (41.3) µg/m3 and mean birthweight 3,292.9 (493.2) grams. Total personal PM2.5 was not associated with birthweight (β= 0.28, 95% CI: -1.93 – 2.49, per 1-unit increase in PM2.5). However, the effect of PM2.5 varied by window opening (none or little of the time: 3.09 (-0.67, 6.86) vs most or all of the time: -1.48 (-4.22, 1.27), interaction p=0.052) and marginally by time spent indoors per day (12 hrs: -1.28 (-4.50, 1.95), 13-18 hrs: 1.19 (-4.02, 6.39), 19+ hrs: 3.32 (-0.86, 7.49), interaction p=0.234). CONCLUSIONS:While we did not find a significant association between total prenatal personal PM2.5 exposure and birthweight, we did find evidence that outdoor source contributions to personal PM2.5 exposure were more strongly associated with lower birthweight. KEYWORDS: air pollution, particular matter, birth outcomes, pregnancy outcomes, epidemiology
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