Gestational transient
thyrotoxicosis (GTT) is defined as transient
thyrotoxicosis caused by the stimulating effect of
human chorionic gonadotropin (hCG) during pregnancy. We attempted to identify the serum hCG level that causes GTT, and we compared the serum hCG levels and
thyroid hormone levels of GTT patients according to whether they had a background of
thyroid disease. We also evaluated serum hCG as a parameter for differentiating between active
Graves' disease (GD) and GTT. We reviewed the 135 cases of pregnant women who came to our hospital to be evaluated for
thyrotoxicosis during their 7th to 14th week of pregnancy, and their serum hCG level was measured at that time. Among the 135 pregnant women with
thyrotoxicosis; 103 of the women had GTT, and the other 32 women had active GD. There were no correlations between their serum hCG levels and free
thyroid hormone levels. There were no significant differences in
thyroid hormone levels or hCG levels among the GTT groups with different
thyroid disease backgrounds; i.e., the GTT group without
thyroid disease, GTT group with
chronic thyroiditis, GTT group with non-functioning
thyroid nodules, and GTT group with GD in remission. The serum hCG level of the GTT group was significantly higher than in the active GD group, but it was not a good parameter for differentiating between the two groups. The FT3/FT4 ratio of the active GD was significantly higher than in GTT group, and was a better parameter for differentiation.