Perinatal Exposure to Air Pollution Linked to Newborn Thyroid Function

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Changes in maternal thyroid function during pregnancy can affect fetal growth, metabolism, and neurodevelopment.
Changes in maternal thyroid function during pregnancy can affect fetal growth, metabolism, and neurodevelopment.

Increases in prenatal exposure to air pollution particulate matter are associated with higher total thyroxine concentrations in newborns, particularly when the exposure occurs in early and mid-pregnancy, according to a study published in JAMA Network Open.

Researchers in the current cohort study investigated the associations between prenatal exposure to air pollutants and newborn thyroid function and identified critical windows of exposure. They used pregnancy and birth data from 1994 to 1997 for 2050 Children's Health Study participants who had complete monthly exposure measures for one or more air pollutants throughout pregnancy. Investigators used the California Line Source Dispersion model to determine monthly prenatal averages of traffic-related air pollutant exposures as well as inverse distance-squared weighting of central monitoring data to determine monthly prenatal averages of ambient air pollutant exposures.

Retrospective measures of newborn total thyroxine via heel-stick blood spots were acquired from the California Department of Public Health. The newborns were 58.6% Hispanic white (n=1202), 31.1% non-Hispanic white (n=638), 3.2% black (n=66), and 7.0% other races/ethnicities (n=144). Of the total newborns, 50.5% were boys and 49.5% were girls.

The mean standard deviation (SD) total thyroxine measure for newborn participants was 16.2 (4.3) μg/dL. In covariate-adjusted linear regression models, a 2-SD increase in prenatal particulate matter with a diameter of <2.5 μm [PM2.5] was associated with a 1.2 μg/dL higher total thyroxine measure (95% CI, 0.5-1.8 μg/dL), and a 2-SD increase in prenatal particulate matter with a diameter of <10 μm [PM10] was associated with a 1.5 μg/dL (95% CI, 0.9-2.1 μg/dL) higher total thyroxine measure. Other air pollutants were not consistently associated with newborn total thyroxine.

PM2.5 exposure had the greatest impact on total thyroxine when it took place in months 3 to 7 of pregnancy, and PM10 exposure had the greatest impact on total thyroxine when it took place in months 1 to 8 (P <.05 for both). The strongest association was observed between PM2.5 and total thyroxine during month 5 of pregnancy, and the strongest PM10 association with total thyroxine at month 1 of pregnancy.

Study investigators conclude that the findings do suggest prenatal exposure to particulate matter in air pollution is associated with higher concentrations of total thyroxine. In addition, “Although PM10 exposure throughout most of pregnancy was associated with higher newborn [total thyroxine] concentrations, PM2.5 exposure in midpregnancy only was associated with higher newborn [total thyroxine] concentrations. Prenatal nitrogen dioxide, ozone, and traffic-related air pollution exposures were not consistently associated with newborn [total thyroxine] concentrations.”

Reference

Howe CG, Eckel SP, Habre R, et al. Association of prenatal exposure to ambient and traffic-related air pollution with newborn thyroid function: findings from the Children's Health Study. JAMA Network Open. 2018; 1(5):e182172. doi: 10.1001/jamanetworkopen.2018.2172

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