Thyroid function and urinary iodine excretion in pregnant women at Jakkart, Nakornrajasima, Thailand

Abstract

In Thailand, the prevalence of IDD of 37 % (n = 4500) in pregnant women was reported by the Ministry of Public Health in the year 2000. Nakornrajasima Province is located in the Northeastern of the country which is an area of iodine deficiency problems. The purpose of this study was to determine thyroid function in 350 of the normal pregnancies at the clinics of Jakkarat Hospital. Demographic data were collected for each subject. Urinary and venous blood samples were taken in various trimesters. Serum TSH and FT4,FT3 levels were measured by using in house IRMA and DPC solid-phase RIA method, respectively. Urine iodine was analyzed by modified ammonium persulfate. The median and interquatile range of TSH concentration was increased from the first trimester of 0.911(0.46-1.31) mIU/L to the second trimester of 1.20(0.88- 1.84) mIU/L and the third trimester of 2.02(1.34-4.45) mIU/L. In contrast, both FT4 and FT3 concentration were decreased from the first to the second and the third trimester of pregnancy. The FT4 values were 1.32(1.20-1.60), 1.25(1.09-1.42) and 1.15(1.04-1.34) ng/dl, while FT3 were 3.42(2.80-4.10), 3.17(2.30-4.0) and 2.27(1.05- 3.08) pg/ml respectively. Urine iodine concentration throughout pregnancy were 297.11(119.80-358.00), 396.62(128.16-481.96) and 375.44(181.58-616.86) μg/L respectively and higher than reference range. In conclusion, the present study demonstrates that the women who received iodated salt (1:20000) during pregnancy showed high normal mean ± SD values of TSH but low normal FT3 and FT4 while UI was higher than normal in the third trimester. The highest degree of correlation between the FT3 and TSH was found (r = -0.593, P<0.01, y = 3.136-0.316x). This suggested that UI determination alone gives inadequate information. Serum FT3 and TSH seems to be an important determinant of mechanism of thyroid gland response to ensure the extra iodine needed by the growing fetus.