Effect of Thiocyanate on Iodine Status of Pregnant Women

The aim of this study was to assess the thyroid status of pregnant women on the basis of biochemical indicators and to evaluate the potential risk of developing iodine deficiency as a result of tobacco smoke exposure by assessing the association between urinary thiocyanate levels and the manifestation of iodine deficiency. The study included 219 pregnant women from the town of Plovdiv and Plovdiv District in Southern Bulgaria. The levels of urinary iodine, thyroid-stimulating hormone (TSH), free thyroxine (FT4), and urinary thiocyanate as indicators of tobacco smoke exposure were measured. Most of the pregnant women (60.1 %) were found to have iodine deficiency, 10.6 % of them had TSH values greater than 4 mIU/L, and 16.4 % had FT4 below 9 pmol/L. There were negative correlations between urinary iodine levels and thiocyanate/creatinine ratio (R = -0.148, р = 0.034) and between thiocyanate/creatinine ratio and FT4 (R = -0.379, p < 0.0001); thiocyanate/creatinine ratio and serum TSH were positively correlated (R = 0.169, p = 0.019). Logistic regression analysis showed that pregnant women in whom the thiocyanate/creatinine ratio was greater than the median value of 3.57 mg/g had a 3.882-fold higher risk of developing iodine deficiency (urinary iodine <150 μg/L) than the pregnant women with lower thiocyanate levels (OR = 3.882, 95 % CI 1.402-10.751, p = 0.009). Higher levels of urinary thiocyanate were found in women exposed to tobacco smoke, and quantification of these ions in urine provided a fast non-invasive method to monitor thiocyanate load. Due to the competitive inhibition of iodine intake by thiocyanates, their levels should be carefully monitored, especially in cases of severe iodine deficiency.