Prenatal exposure to prescribed smoke PM_2.5 and low birth weight in Georgia, USA

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.

This study investigated the association between prenatal exposure to PFS-specific PM_2.5 and birth weight in Georgia, USA.

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.

Higher PFS PM_2.5 exposure was independently associated with lower birth weight. Each 1 µg/m³ 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/m³) of PFS PM_2.5 during the entire gestation corresponded to an 11.70 g (95 % CI: 0.95, 22.45) reduction.

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.