Environment/Climate Change
Effect of extreme heat exposure on the associations between weekly gestational exposure to fine particulate matter and preterm birth in a North Carolina birth cohort Alison K. Krajewski* Alison K. Krajewski Breanna Alman Ambarish Vaidyanathan Thomas J. Luben Kristen M. Rappazzo
Preterm birth (PTB;<37 weeks completed gestation) is associated with exposure to fine particulate matter (PM2.5). Recent studies suggest that extreme heat events (EHE) may further impact this association. We estimated the associations between PM2.5 and PTB, with different metrics for EHE. We examined the associations between gestational exposure to PM2.5 and PTB in a North Carolina birth cohort (N=552,567) from 2011-2015. Daily (24-hour average) PM2.5 concentrations from US Environmental Protection Agency’s Fused Community Multiscale Air Quality Modelling System (fCMAQ) model were linked to a residential address at delivery, then averaged across each week of pregnancy, trimester, and entire pregnancy. A census tract indicator of EHE (maximum daily heat index above the 95th percentile for two consecutive days) was linked for the same time period. Modified Poisson regressions with robust errors were used to estimate risk differences (RDs) in PM2.5 per 10,000 births, adjusted for gestational parent race/ethnicity, age at delivery, Medicaid status, and rural-urban commuting area. Additional models included a dichotomous indicator of EHE (0 events, 1 or more events) as a co-exposure or an interaction term. The median PM2.5 concentration during pregnancy was 9.55 µg/m3, and PTB prevalence was 7.3%. The median number of EHE during pregnancy was 5 (range: 0-31). Overall, there were negative associations between PM2.5 and PTB, without adjustment for EHE (RDs ranged from -17 to -4), with adjustment for EHE (RDs ranged from -19 to 30), and with interaction (RDs ranged from -16 to -2). The strongest associations with EHE were in the third trimester, without PM2.5 [RD -226 (95% CI: -240, -212)], with PM2.5 [RD -282 (-297, -267)], and with interaction [-1022 (-1138, -906)]. Overall, we observed negative associations with gestational exposure to PM2.5 and PTB, with no evidence of interaction with EHE.