Associations between PM2.5 and term low birth weight in a North Carolina cohort and effect modification by extreme heat events

Abstract

BACKGROUND AND AIM: Low birth weight (LBW) can be an indicator for poor health outcomes, including neonatal mortality, and may be caused by environmental exposures. Previously, exposure to high ambient temperatures was linked with increased odds of LBW, while results looking at fine particulate matter (PM₂.₅) exposure have been mixed. Our objective is to determine if a relationship exists between PM₂.₅ exposure during pregnancy and term LBW and then to see if that relationship is modified by concurrent exposure to extreme heat events. METHODS: We used North Carolina birth registry data linked to exposure data using geocoded addresses obtained from the birth records (2002-2015) for live, full-term (≥37 weeks gestation), singleton births (n=1,280,064). LBW was defined as weighing 2,500g. PM₂.₅ concentrations were obtained using EPA’s CMAQ downscaler and were averaged over trimester and entire pregnancy. Extreme heat events were defined as a census-tract specific daily maximum heat index 95th percentile for at least 2 consecutive days. We computed census-tract specific 95th percentiles using heat index data for the summer months (1981–2010). For inclusion in a trimester analysis, portions of that trimester had to occur between May-September. We estimated risk differences (RD) and 95% confidence intervals (CI) with interaction terms for total number of extreme heat events during the corresponding exposure period, adjusting for Medicaid and maternal age. RESULTS:We observe generally null relationships between PM₂.₅ and term LBW for all trimesters (RD per 10,000 [95% CI]) ranged from -1 [-8, 6] to 1 [-5, 6]) and the pregnancy (1 [-5, 8]). These results persisted when extreme heat events were included as an interaction term (Pregnancy:1 [-5, 8]). CONCLUSIONS:Preliminary analyses did not indicate a relationship between PM₂.₅ and term LBW or effect measure modification by extreme temperature days. This abstract does not reflect CDC, ATSDR, or EPA policy. KEYWORDS: Air pollution, birth outcomes, particulate matter, climate, environmental epidemiology