Associations between traffic-related air pollutants and preterm birth in a North Carolina birth cohort, 2003-2015

Abstract

Background and Aim: Preterm birth (PTB; <37 weeks completed gestation) is associated with exposure to fine particles and ozone, but less is known about associations with nitrogen dioxide (NO₂) and other traffic-related air pollutants, such as benzene, toluene, ethylbenzene, and xylene (BTEX). We estimated the associations between PTB and NO₂, with and without adjustment for BTEX. Methods: We examined the associations between PTB and gestational exposure to NO₂ in a North Carolina singleton birth cohort (N=1,367,507) from 2003-2015. Daily 8-hour max NO₂ concentrations from a hybrid-model with a spatial resolution of 1km² were aggregated to census tracts and linked to residential address at delivery, then averaged across each week of pregnancy. We obtained annual average ambient concentrations for BTEX for census tracts from the 2011 National Air Toxics Assessment. Modified Poisson regression models with robust errors were used to estimate risk differences (RD(95% CIs)) per 10-ppb increase in NO₂, adjusted for gestational parent marital status, race/ethnicity, age at delivery, Medicaid status, month of conception, and BTEX. Results: The median (IQR) NO₂ across each day of pregnancy was 15.0(10.2) ppb and 1.6(1.1) ppb for BTEX. The associations between NO₂ and PTB were of similar magnitude across each week of gestation. RDs with and without adjustment for BTEX varied. RDs per 10-ppb increase NO₂ exposure during each week of gestation ranged from -7(95% CI: -14,1) in weeks 17 and 23 to 0(-6,5) in week 36 per 10,000 births, respectively. Adjusting for BTEX, RDs ranged from 19(13,25) in week 36 to 36(27,44) in week 24 per 10,000 births, respectively. Conclusions: While the association between NO₂ exposure and PTB were generally null across each week of gestation, when adjusting for BTEX, we observed a consistent pattern of increased risk of PTB with NO₂ exposure. Keywords: air pollution, preterm birth, nitrogen dioxide, reproductive outcomes