Air Pollution and Preterm Birth: Comparing average and repeated peak exposure metrics in a North Carolina birth cohort, 2003-2015 (Abstract)
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Exposures to ambient air pollutants during pregnancy are associated with preterm birth (PTB) in studies that average pollutant concentrations during critical windows. We evaluated the association between ozone (O3) or particulate matter <2.5 micrometers (PM2.5) during pregnancy and PTB using continuous and categorical metrics of average and repeated peak exposure.
We analyzed data from North Carolina (NC) birth certificates linked to the NC Birth Defects Monitoring Program, limited to live singleton births without defects and delivered from 2003-2015. The Community Multiscale Air Quality Modeling System (CMAQ) was used to assign average and daily peak exposures to O3 (daily 8-hour maximum) and PM2.5 (24-hour average) at different daily threshold concentrations (O3: 55-70 ppb; PM2.5: 20-35 µg/m3) during trimesters 1 and 2 of pregnancy. Descriptive statistics, including weighted kappa statistics, were evaluated. Modified Poisson regression models were used to estimate adjusted risk differences (aRD) per 10,000 births.
Among the sample of 1,414,287 births, 8.4% were PTB. The number of repeated peak exposures ranged from 0 to 16+ days over different threshold concentrations during trimester 1 or 2. There was slight to moderate agreement between average and repeated peak exposures, with decreased agreement as threshold concentrations increased. aRDs ranged from -28 to 21 for average O3 exposure and from -90 to 90 for repeated O3 exposure. aRDs ranged from 12 to 113 for average PM2.5 exposure and from -276 to 123 for repeated PM2.5 exposure. This study provides insights into heterogeneity in risk of PTB when using different air pollution exposure metrics.