Association Between Organophosphate Pesticide Exposure and Thyroid Hormones in Pregnant Women

Background: Use of organophosphate pesticides (OPs) is widespread in China. Although animal studies suggested that OP exposure could affect thyroid function, little is explored in human populations. Methods: We investigated levels of OP exposure in pregnant women and the relationship between OPs and thyroid hormones in Shandong, China. We enrolled 637 pregnant women from April 2011 to December 2013. OP exposure was assessed by a questionnaire administered to the pregnant women in the hospital and by analyses of urinary dialkylphosphate (DAP) metabolites of OPs in pregnant women (n = 413). We measured the concentration of five thyroid hormones in serum samples in pregnant women (n = 325) and analyzed the association between DAP metabolites of OPs and thyroid hormones (n = 325). Results: Median levels of DAP metabolites were 9.81 mu g/L for dimethylphosphate (DMP), 0.79 mu g/L for dimethylthiophosphate (DMTP), 5.00 mu g/L for diethylphosphate (DEP), and 0.78 mu g/L for diethylthiophosphate (DETP), which were higher than those reported in developed countries. We found that the total DAP concentration (the sum of DMP, DMTP, DEP, and DETP) in urine was positively associated with free T4 levels (beta = 0.137; 95% confidence interval [CI] = 0.012, 0.263) and negatively associated with thyroid-stimulating hormone levels (beta = -0.145; 95% CI = -0.242, -0.048). Conclusions: The findings suggest that OP exposure may be associated with changes in thyroid function in pregnant women. Given that urinary OP levels in pregnant women in Shandong were much higher than those reported in developed countries, further studies on the effects of OP exposure on thyroid function in pregnant women in China are warranted.