Weekly prenatal PM2.5 and NO2 exposures in preterm, early term, and full term infants: Decrements in birth weight and critical windows of susceptibility

Abstract

Background: Previous studies have observed associations between birth weight and prenatal air pollution exposure, but there is not consensus on timing of critical windows of susceptibility.

Objective: We estimated the difference in birth weight among preterm, early term and full term births associated with weekly exposure to PM_2.5 and NO₂ throughout gestation.

Methods: We included all singleton live births in the Lower Peninsula of Michigan (United States) between 2007 and 2012 occurring at or after 32 weeks gestational age (n = 497,897). Weekly ambient PM_2.5 and NO₂ concentrations were estimated at maternal residences using 1-km gridded data from ensemble-based models. We utilized a distributed lag nonlinear model to estimate the difference in birth weight associated with weekly exposures from the last menstrual period (week 0) through 31 weeks gestation for preterm births; through 36 weeks gestation for early term births; and through 38 weeks gestation for full term births.

Results: In single-pollutant models, a 5 μg/m³ increase in PM_2.5 exposure was associated with a reduction in birth weight among preterm births (-37.1 g [95% confidence interval [CI]: 60.8 g, -13.5 g]); early term births (-13.5 g [95% CI: 26.2 g, -0.67 g]); and full term births (-8.23 g [95% CI: 15.8 g, -0.68 g])]. In single-pollutant models, a 10 ppb increase in NO₂ exposure was associated with a -11.7 g (95% CI: 14.46 g, -8.92 g) decrement in birth weight among full term births only. In models co-adjusted for PM_2.5 and NO₂, PM_2.5 exposure was associated with reduced birth weight among preterm births (-36.9 g [95% CI: 61.9 g, -11.8 g]) and NO₂ exposure was associated with reduced birth weight among full term births (-11.8 g [95% CI: 14.7 g, -8.94 g]). The largest decrements in birth weight were associated with PM_2.5 exposure between approximately 10 and 26 weeks of pregnancy; for NO₂ exposure, the largest decrements in birth weight in full term births were associated with exposure between weeks 6-18.

Conclusion: We observed the largest and most persistent adverse associations between PM_2.5 exposure and birth weight in preterm infants, and between NO₂ exposure and birth weight in full term infants. Exposure during the first half of pregnancy had a greater impact on birthweight.