The association between perchlorate and thiocyanate exposure and thyroid function in first-trimester pregnant Thai women.

J Clin Endocrinol Metab 2014 Jul 4;99(7):2365-71. Epub 2014 Apr 4.

Departments of Medicine (N.C.) and Obstetrics and Gynecology (C.S., A.C.), Faculty of Medicine, Thammasat University, Pathumthani 10200, Thailand; Department of Medicine (B.O., L.C.), Ramathibodi Hospital, Mahidol University, Bangkok 10400, Thailand; and Department of Medicine (E.N.P., X.H., L.E.B.), Boston University School of Medicine, Boston, Massachusetts 02118-2308.

Context: Thyroid hormone is critical for fetal neurodevelopment. Perchlorate and thiocyanate decrease thyroidal iodine uptake by competitively inhibiting the sodium/iodide symporter. It is clear that perchlorate and thiocyanate anions can influence thyroid function. However, as pollutants in the environment, their impact is conflicting.

Objective: The objective was to determine the effects of environmental perchlorate and/or thiocyanate exposure on thyroid function in first-trimester pregnant women.

Design And Patients: A cross-sectional study was conducted in 200 pregnant Thai women with a gestational age of 14 weeks or less.

Measures: Urinary iodide, perchlorate, thiocyanate, and serum thyroid function tests were measured.

Results: The women were aged 28.6 ± 6.1 years and the mean gestational age was 9.6 ± 2.7 weeks. Median urinary iodide, perchlorate, and thiocyanate concentrations were 153.5 μg/L, 1.9 μg/L, and 510.5 μg/L, respectively. Using Spearman's rank correlation analyses, there were positive correlations between serum TSH and urine perchlorate to creatinine (r = 0.20, P = .005) and TSH and thiocyanate to creatinine ratios (r = 0.22, P = .001). There were negative correlations between free T4 and the perchlorate to creatinine ratio (r = -0.18, P = .01) and free T4 and the thiocyanate to creatinine ratio (r = -0.19, P = .008). In multivariate analyses adjusting for log thiocyanate to creatinine ratio, log iodide to creatinine ratio, and gestational age, log perchlorate to creatinine ratio was positively associated with log TSH (P = .002) and inversely associated with log free T4 (P = .002). Log thiocyanate to creatinine ratio was a significant positive predictor of log TSH (P = .02) in women with a urine iodide level of less than 100 μg/L.

Conclusions: Low-level environmental exposure to perchlorate and thiocyanate is common in Thailand. Low-level exposure to perchlorate is positively associated with TSH and negatively associated with free T4 in first-trimester pregnant women using multivariate analyses. In multivariate analyses, thiocyanate exposure is also positively associated with TSH in a subgroup of pregnant women with low iodine excretion.

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