A comparative study on thyroid function during late pregnancy and of fertile women in iodine excess area

Abstract

To explore the influences of pregnancy and iodine intake on thyroid function and immune functions, 210 pregnant women and 290 fertile women were chosen from iodine excess area, and the average ages of them were (27. 69±4. 73 )and (30. 62±6. 01 )years respectively. Fasting blood and urine were collected in the morning. The urinary iodine level was determined by arsenic-cerium catalytic contact. Serum free triiodothyronine ( FT3 ), free thyroxine ( FT4 ), and sensitive thyroid-stimulating hormone ( sTSH ) levels were measured by chemiluminescence.Thyroid peroxidase antibody (TPOAb)and thyroglobulin antibody (TGAb)were measured by radioimmunoassay. The median urinary iodine in the pregnant and fertile women were I 240. 70 and 949. 21 μg/L, respectively. There were 84. 3% pregnant women and 81.0% fertile women admitting excess iodine intake. The prevalence of overall thyroid diseases was 22. 9% in the pregnant women and 30. 3% in the fertile women. The prevalence of hyperthyroidism,subclinical hyperthyroidism, hypothyroidism, and subclinical hypothyroidism was0. 5%, 1.9%, 0. 5%, and 20. 0% in the former group, and 2. 8%, 0. 3%, 0. 3%, and 26. 9% in the latter. Both FT3 and FT4 levels of the pregnant women were lower than those of fertile women [(4. 03±0. 59 vs 4. 71 ± 1.04)pmol/L, ( 13. 35 ± 1.59 vs 14. 27 ±3.63 )pmol/L,both P＜0. 01], and the positive rate of TGAb of pregnant women was also lower than that of fertile women (7. 1% vs14. 1%, P=0. 014). The prevalence of thyroid diseases and positive rate of thyroid autoantibodies is high in women with excess iodine intake. Compared with fertile women, pregnancy may lead to decreas~s in level of thyroid hormones and positive rate of TGAb. Their iodine intake should be controlled, and the thyroid function and autoimmunity antibodies should be monitored. Key words: Pregnant women; Fertile women; Excess iodine; Thyroid function; Thyroid autoimmunity function