Air Pollution and Term Birth Weight in New York, New York
Air Pollution and Term Birth Weight in New York, New York
Building on a unique exposure assessment project in New York, New York, we examined the relationship of particulate matter with aerodynamic diameter less than 2.5 μm and nitrogen dioxide with birth weight, restricting the population to term births to nonsmokers, along with other restrictions, to isolate the potential impact of air pollution on growth. We included 252,967 births in 2008–2010 identified in vital records, and we assigned exposure at the residential location by using validated models that accounted for spatial and temporal factors. Estimates of association were adjusted for individual and contextual sociodemographic characteristics and season, using linear mixed models to quantify the predicted change in birth weight in grams related to increasing pollution levels. Adjusted estimates for particulate matter with aerodynamic diameter less than 2.5 μm indicated that for each 10-µg/m increase in exposure, birth weights declined by 18.4, 10.5, 29.7, and 48.4 g for exposures in the first, second, and third trimesters and for the total pregnancy, respectively. Adjusted estimates for nitrogen dioxide indicated that for each 10-ppb increase in exposure, birth weights declined by 14.2, 15.9, 18.0, and 18.0 g for exposures in the first, second, and third trimesters and for the total pregnancy, respectively. These results strongly support the association of urban air pollution exposure with reduced fetal growth.
Over the past decade, the literature suggesting possible adverse effects of air pollution on pregnancy has grown considerably. Air pollution may affect pathways involving oxidative stress and chronic inflammation, which are believed to influence the course and outcome of pregnancy. Studies have generated results that support possible adverse effects of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5), particulate matter with aerodynamic diameter less than 10 μm, nitrogen dioxide, and carbon monoxide on fetal growth, preterm birth, preeclampsia, birth defects, and infant mortality. Although the volume and quality of studies have grown considerably, the evidence remains inconclusive.
Several sources of uncertainty limit confidence in the findings. Exposure assessment methods are often based on regulatory monitoring data, which lack the spatial resolution to capture intraurban differences in exposure at the neighborhood or individual level. Air pollution levels are often highest in the most socioeconomically deprived areas, and adjustment for confounding by socioeconomic deprivation is incomplete. Definition of health endpoints varies across studies, which hinders attempts at replication. Finally, data analysis is challenging, with multiple candidate time windows for adverse effects, pregnancy duration that spans seasons with varying exposures, and both temporal and spatial determinants of exposure with differing susceptibility to measurement error and confounding.
We report findings on exposures to PM2.5 and nitrogen dioxide and birth weight among term births from a study with uniquely detailed exposure assessment data from the New York City Community Air Survey (NYCCAS). NYCCAS data, which provide far greater spatial resolution than was available in previous birth outcome studies, were linked to individual addresses for a large number of births in a setting where lower socioeconomic status is not associated with higher air pollution exposure, reducing the potential for confounding.
Abstract and Introduction
Abstract
Building on a unique exposure assessment project in New York, New York, we examined the relationship of particulate matter with aerodynamic diameter less than 2.5 μm and nitrogen dioxide with birth weight, restricting the population to term births to nonsmokers, along with other restrictions, to isolate the potential impact of air pollution on growth. We included 252,967 births in 2008–2010 identified in vital records, and we assigned exposure at the residential location by using validated models that accounted for spatial and temporal factors. Estimates of association were adjusted for individual and contextual sociodemographic characteristics and season, using linear mixed models to quantify the predicted change in birth weight in grams related to increasing pollution levels. Adjusted estimates for particulate matter with aerodynamic diameter less than 2.5 μm indicated that for each 10-µg/m increase in exposure, birth weights declined by 18.4, 10.5, 29.7, and 48.4 g for exposures in the first, second, and third trimesters and for the total pregnancy, respectively. Adjusted estimates for nitrogen dioxide indicated that for each 10-ppb increase in exposure, birth weights declined by 14.2, 15.9, 18.0, and 18.0 g for exposures in the first, second, and third trimesters and for the total pregnancy, respectively. These results strongly support the association of urban air pollution exposure with reduced fetal growth.
Introduction
Over the past decade, the literature suggesting possible adverse effects of air pollution on pregnancy has grown considerably. Air pollution may affect pathways involving oxidative stress and chronic inflammation, which are believed to influence the course and outcome of pregnancy. Studies have generated results that support possible adverse effects of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5), particulate matter with aerodynamic diameter less than 10 μm, nitrogen dioxide, and carbon monoxide on fetal growth, preterm birth, preeclampsia, birth defects, and infant mortality. Although the volume and quality of studies have grown considerably, the evidence remains inconclusive.
Several sources of uncertainty limit confidence in the findings. Exposure assessment methods are often based on regulatory monitoring data, which lack the spatial resolution to capture intraurban differences in exposure at the neighborhood or individual level. Air pollution levels are often highest in the most socioeconomically deprived areas, and adjustment for confounding by socioeconomic deprivation is incomplete. Definition of health endpoints varies across studies, which hinders attempts at replication. Finally, data analysis is challenging, with multiple candidate time windows for adverse effects, pregnancy duration that spans seasons with varying exposures, and both temporal and spatial determinants of exposure with differing susceptibility to measurement error and confounding.
We report findings on exposures to PM2.5 and nitrogen dioxide and birth weight among term births from a study with uniquely detailed exposure assessment data from the New York City Community Air Survey (NYCCAS). NYCCAS data, which provide far greater spatial resolution than was available in previous birth outcome studies, were linked to individual addresses for a large number of births in a setting where lower socioeconomic status is not associated with higher air pollution exposure, reducing the potential for confounding.