Hyper-localized measures of air pollution and risk of preterm birth in Oakland and San Jose, California

Abstract

Background: US preterm-birth rates are 1.6 times higher for Black mothers than for White mothers. Although traffic-related air pollution (TRAP) may increase the risk of preterm birth, evaluating its effect on preterm birth and disparities has been challenging because TRAP is often measured inaccurately. This study sought to estimate the effect of TRAP exposure, measured at the street level, on the prevalence of preterm birth by race/ethnicity.

Methods: We linked birth-registry data with TRAP measured at the street level for singleton births in sampled communities during 2013-2015 in Oakland and San Jose, California. Using logistic regression and marginal standardization, we estimated the effects of exposure to black carbon, nitrogen dioxide and ultrafine particles on preterm birth after confounder adjustment and stratification by race/ethnicity.

Results: There were 8823 singleton births, of which 760 (8.6%) were preterm. Shifting black-carbon exposure from the 10th to the 90th percentile was associated with: 6.8%age point higher risk of preterm birth (95% confidence interval = 0.1 to 13.5) among Black women; 2.1%age point higher risk (95% confidence interval = -1.1 to 5.2) among Latinas; and inconclusive null findings among Asian and White women. For Latinas, there was evidence of a positive association between the other pollutants and risk of preterm birth, although effect sizes were attenuated in models that co-adjusted for other TRAP.

Conclusions: Exposure to TRAP, especially black carbon, may increase the risk of preterm birth for Latina and Black women but not for Asian and White women.

Keywords: Air pollution; health disparities; preterm birth.

Figure 1

Distribution of pollutants for pregnant women delivering live-born neonates between 2013 and 2015 in Oakland and San Jose, California. Dashed lines correspond to the 10th and 90th percentiles of the distribution across all four races/ethnicities. The distribution of ultrafine particles excludes one outlier that equals 205 from this visual display.

Figure 2

Spatial distribution of black carbon (BC), nitrogen dioxide (NO₂) and ultrafine particles (UFP) in Oakland and San Jose, California (CA)

Figure 3

Estimated risk differences and 95% confidence intervals for preterm birth associated with setting exposure to traffic-related air pollutants at high vs low levels for pregnant women in Oakland and San Jose, California, 2013–2015. These risk differences correspond to the estimated change in absolute risk of preterm birth (in percentage points) comparing risk when each pollutant exposure is set to the 90th percentile of its empirical distribution in this cohort vs the 10th percentile of the same distribution. Positive risk differences imply that increasing levels of the pollutant are associated with higher risks of preterm birth and negative differences imply that increasing levels of the pollutant are associated with lower risks of preterm birth. Refer to Supplementary Table S1, available as Supplementary data at IJE online, for the description of each model.