Variations of thyroid hormone levels in pregnant women with different iodine nutrition and in different stages of gestation

Objective To investigate the variations of thyroid hormone levels and status of thyroid function in pregnant women with different iodine nutrition status and in stages of gestation in Beihai.Methods Free triiodothyronine(FT3),free thyroxine(FT4),thyroid stimulating hormone(TSH) and human choronic gonadotropin(hCG) were determined in 623 pregnant women by ACS-180 automatic chemiluninescence analyzer.The urinary iodine content in a random urination was measured using cold digestion method of rapid quantitative detection urinary iodine according to iodine catalytic effect of Arsenic-Cerium.Results Serum FT3,FT4 and hCG levels in the first and second trimesters were higher than those in the third trimester(P0.05),and TSH levels were lower than those in the third trimester(P0.05).FT3,FT4 and hCG levels were lower in high urine iodine group than in normal and low urine iodine groups(P0.05).No significant differences were found in the 3 groups(P0.05).The incidence of thyroid dysfunction was 7.54%,with no significant differences between the gestation stages and urine iodine groups(P0.05).The incidence of subclinical hyperthyroidism and subclinical hypothyroidism was 3.53% and 2.57%,respectively and the incidence of hyperthyroidism and hypothyroidism was 1.12% and 0.32%,respectively.The incidence of subclinical hyperthyroidism was dominant in the urinary iodine groups,while in the first and third trimesters,the incidence of subclinical hypothyroidism prevails in the second trimester.Conclusion The iodine nutrition conditions and the variations of hCG levels during pregnancy were not the major factors contributing to thyroid dysfunction,which might be initiated by the changes of materno-fetal immunity during pregnancy.