[TBG, TSH and thyroid hormones in fetus].

In this study, we measured cord serum thyroxine (T4), triiodothyronine (T3), reverse T3 (rT3), thyroxine binding globulin (TBG) and thyroid-stimulating hormone (TSH) in 37 fetuses (29-42 gestational weeks). The mean cord serum TBG was 18.2 +/- 3.2 mg/dl (mean +/- S.E., n = 37) and there was no correlation between cord serum TBG levels and gestational weeks. The cord serum T3 levels increased with advancing gestational weeks. On the other hand, cord serum rT3 levels decreased with advancing gestational weeks. There was a significant positive correlation between the TBG and T4 levels after 32 gestational weeks (n = 34, r = 0.545, p less than 0.001), and between the TBG and T3 levels (n = 36, r = 0.65, p less than 0.001). There was a significant positive correlation between the TBG and T3 levels after 37 gestational weeks (n = 24, r = 0.43, p less than 0.05). The cord serum TSH levels had a significant difference (p less than 0.05) between preterm fetus (n = 11, 12.8 +/- 2.2 mU/ml, mean +/- S.E.) and term fetus (n = 25, 8.2 +/- 0.8 mU/ml). The T4/TSH ratio in the preterm fetus (0.65 +/- 0.01) was significantly smaller (p less than 0.001) than that of term fetus (1.60 +/- 0.16). These results suggest that thyroid hormones are closely related with TBG in fetus and the sensitivity of the thyroid gland to TSH may increase with advancing gestational weeks.