Associations between exposure to Air Pollution and Congenital Hypothyroidism

Abstract

Background: Adequate thyroid hormone (TH) availability is required for optimal development of the fetal brain. Untreated permanent congenital hypothyroidism (CHT) typically results in intellectual disability in humans. Newborns with transient-CHT have temporary TH deficiency and will improve to normal TH levels usually in few months.Aims: To estimate the associations of prenatal exposure to particulate matter (PM) with CHT and transient-CHT in newborns.Methods: A historical birth cohort study, based on the Israeli national program for neonatal screening, including term infants born in Israel in 2009-2015 (N=696,461). Separate logistic regression models were used to estimate the associations of PM as a continuous variable with CHT and transient-CHT, adjusted for ethnicity, calendar month and year of conception, socioeconomic status, and sub-district. To assess residual confounding, postnatal exposures to the same pollutants were used as negative control exposures. These pollutants are impacted by the same potential unmeasured confounders, but should have null relationship with the outcome in mutually adjusted models, if there are no substantial unmeasured confounders.Results: First and second trimester exposure to PM2.5, and third trimester exposure to PM2.5-10, were associated with CHT (adjusted-OR: first and second trimester PM2.5: 1.12, 95% CI: 1.00-1.27; and 1.10, 0.99-1.22, respectively; third trimester PM2.5-10: 1.18, 95% CI: 1.07-1.29). No evidence of residual confounding was noted. Exposure to PM2.5-10 during the first and second trimester were associated with transient-CHT (adjusted-OR = 1.42, 95% CI: 1.10-1.83; and 1.27, 0.95-1.69, respectively), with no evidence of residual confounding.Conclusions: Exposure to PM2.5 and PM2.5-10 in specific trimesters of pregnancy are associated with increased risk of CHT and transient-CHT. Negative control analyses applied to this study support a causal interpretation of these findings. Additional studies are needed to refine the exact timing of these effects, quantify associations with additional pollutants, and explore possible biological mechanisms.