Objective: To investigate the prevalence of gestational transient thyrotoxicosis (GTT) and analyze the cause of thyrotoxicosis encountered in this period.
Methods: An epidemiologic survey in ten hospitals in Shenyang was performed and 534 pregnant women during the first trimester of pregnancy filled questionnaire, received physical examination and had serum thyroid-stimulating hormone (TSH), free T(4) (FT(4)), free T(3) (FT(3)), thyroid peroxidase antibody (TPOAb), thyrotrophin receptor antibody (TRAb), and human chorionic gonadotrophin (hCG) tests.
Results: (1) The total prevalence of thyrotoxicosis was 9.75% (52/534) in the first trimester and the prevalence of GTT was 7.86%, which accounted for 80.77% of the thyrotoxicosis encountered in this period. A total of 88.89% of the overt GTT showed only elevated FT(3) level. (2) The level of serum hCG increased gradually in the first trimester. The medians of hCG were 25 300, 85 220 and 81 780 IU/L 6, 8 - 10 and 12 weeks after gestation, respectively (P = 0.000). The medians of serum TSH were 1.45, 1.10 and 0.84 mIU/L 6, 8 - 10 and 12 weeks after gestation, respectively (P < 0.01). (3) When serum hCG was more than 50 000 IU/L, the prevalence of GTT increased obviously. When serum hCG was between 80 000 IU/L and 110 000 IU/L, subclinical GTT increased significantly. When serum hCG was more than 110 000 IU/L, overt GTT increased significantly. Correlation analysis showed that serum hCG was related negatively with TSH (r = -0.402, P = 0.000) and positively with FT(3) (r = 0.165, P = 0.000), but not related with FT(4).
Conclusions: The prevalence of GTT is 7.86% in the first trimester and it is the main cause of thyrotoxicosis found in the first trimester, accounting for 80.77% of all the causes. The serological characteristic of overt GTT is mainly the elevation of serum FT(3) level. Serum hCG level is related with the severity of GTT.