High traffic roads and adverse birth outcomes: comparing births upwind and downwind of the same road

Abstract

Traffic-related air pollution is a major concern for perinatal health. Determining causal associations, however, is difficult because high-traffic areas tend to correspond with lower socioeconomic neighborhoods and other environmental exposures. To overcome confounding, we compared pregnant individuals living downwind and upwind of the same high-traffic road. We leveraged vital statistics data for Texas from 2007 to 2016 (n = 3 570 272 births) and computed hourly wind estimates for residential addresses within 500 m of high-traffic roads (ie, annual average daily traffic >25 000 vehicles) (10.9% of births). We matched pregnant individuals predominantly upwind with pregnant neighbors downwind of the same road segment (n = 37 631 pairs). Living downwind was associated with a decrease of 11.6 g (95% CI, -18.01 to -5.21) in term birth weight. No associations were observed with low term birth weight, preterm birth, or very preterm birth. In distance-stratified models, living downwind within 50 m was associated with a decrease of 36.3 g (95% CI, -67.74 to -4.93) in term birth weight and living 51-100 m downwind was associated with an odds ratio of 3.68 (95% CI, 1.71-7.90) for very preterm birth. These results suggest traffic air pollution is associated with adverse birth outcomes, with steep distance decay gradients around major roads. This article is part of a Special Collection on Environmental Epidemiology.

Keywords: air pollution; birth outcomes; instrumental variable; traffic; wind.

Figure 1

Estimating wind exposure and building shielding at a maternal residence. (A) Wind direction is converted into a 31° interval. All objects within the interval are classified as upwind of the residence. (B) Hourly intervals are summed over the length of pregnancy, creating 360 radial segments. To protect cohort privacy, intervals are summed over 2018 for US Environmental Protection Agency air monitor EP_10-march 1, 2004. (C) Radial segments were spatially joined to road networks to estimate hours for each road. Segment was upwind from residence. (D) Buildings between roads and the residence contributed to building shielding. The radii for all circles are 500 m. Variables in B-D are colored by quantile.

Figure 2

Matching downwind and upwind residences in Texas from 2007 to 2016. (A) Matching maximizes the similarity in distance to road between exposed (downwind) and control (upwind) residences. (B) Matched residences are mostly neighbors on opposite sides of a high-traffic road.