Effect measure modification of the association between air pollution and birth defects by neighborhood deprivation, North Carolina 2011-2015
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About 3% of babies born in North Carolina (NC) are diagnosed with a birth defect. The objective of this study was to evaluate whether associations between gestational exposure to fine particulate matter (PM2.5) during the first trimester and birth defects were modified by neighborhood deprivation in a NC birth cohort from 2011-2015. Modeled daily PM2.5 concentrations from EPA’s Community Multiscale Air Quality (CMAQ) model were aggregated to census tract, and linked to residential address at delivery, and then averaged across the first trimester to estimate exposure. The Neighborhood Deprivation Index (NDI) was created using principal component analysis with census variables representing income/poverty, education, employment, housing, and occupation; with NDI dichotomized into high and low deprivation at the median. Linear binomial regression models were used to estimate prevalence differences (PDs) of PM2.5 per 10,000 births stratified by high or low NDI categories, adjusted for education and gestational parent race/ethnicity. Of the 566,799 births, 3.12% had at least one birth defect, 479 had pulmonary valve atresia/stenosis, 245 had tetralogy of Fallot (TOF), 299 had atrioventricular septal defects, 80 had lower limb reduction defects and 213 had gastroschisis. The daily median PM2.5 concentration during trimester 1 was 9.45 µg/m3 among those in low NDI neighborhoods and 9.36 µg/m3 among those in high NDI neighborhoods. The adjusted PDs for PM2.5 and birth defects were not significant for the birth defects examined in this population and the estimates were similar between high and low NDI groups except for TOF which had a negative PD estimate for those in low NDI neighborhoods and a positive PD for those on high NDI neighborhoods. While power is limited, the potential separation of effects may suggest increased birth defects in high deprivation areas, which warrants further study with larger case numbers.