Prenatal exposure to prescribed smoke PM2.5 and low birth weight in Georgia, USA

Background Prescribed burning is a major but poorly characterized source of fine particulate matter (PM 2.5 ) in the southeastern United States. While wildfire-related smoke PM 2.5 has been linked to adverse birth outcomes, evidence on prescribed fire-related smoke (PFS) and birth weight remains limited, particularly in the Southeast. Objective This study investigated the association between prenatal exposure to PFS-specific PM 2.5 and birth weight in Georgia, USA. Methods We analyzed 448,477 singleton term births (37–42 weeks of gestation) with last menstrual period (LMP) dates between January 1, 2013 and December 31, 2016. Daily ZIP code-level PFS PM 2.5 concentrations were averaged over early gestation (first 4 and 6 weeks), each trimester, and the entire pregnancy. High-exposure metrics were defined as the number of days exceeding percentile-based thresholds for each exposure window. Linear regression models adjusted for non-PFS PM 2.5 , LMP date, gestational age, infant sex, and maternal characteristics. Results Higher PFS PM 2.5 exposure was independently associated with lower birth weight. Each 1 µg/m 3 increase in average PFS PM 2.5 during the first 4 weeks and the first trimester was associated with birth weight decreases of 3.22 g (95 % confidence interval [CI]: 0.82, 5.62) and 4.56 g (95 % CI: 0.12, 9.00), respectively. Each additional day exceeding the 95th percentile (1.21 µg/m 3 ) of PFS PM 2.5 during the entire gestation corresponded to an 11.70 g (95 % CI: 0.95, 22.45) reduction. Conclusion Prenatal PFS exposure may reduce birth weight, particularly during early pregnancy, and both exposure intensity and duration are important in evaluating the health impacts of fire-related PM 2.5 .