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Effect of administration of thyroxine on the risk of postpartum recurrence of hyperthyroid Graves' disease.

In our previous study, we reported that the administration of T4 to patients with Graves' disease who were under treatment with methimazole (MMI) decreased the level of antibodies to thyroid-stimulating hormone (TSH) receptors and the rate of recurrence of hyperthyroidism. In this study, the effect of T4 administration on the rate of postpartum recurrence of hyperthyroidism was examined. Seventy-eight patients with Graves' disease had been treated with MMI for 1-3 yr before pregnancy, and MMI was discontinued 5-6 months after the onset of pregnancy because the levels of antibodies to TSH receptors decreased during early pregnancy. The patients were then divided into two groups. Group A (n = 40) was given T4 (100 micrograms/day) and group B (n = 38) was not given any drugs from 5 months after the onset of pregnancy until 1 yr after delivery. The levels of the antibodies to TSH receptors and serum concentrations of thyroxine-binding globulin (TBG) and T4 were not different between the two groups before and during pregnancy, although a transient increase in serum T4 and TBG concentrations were observed during the pregnancy in both groups. After delivery, levels of antibodies to TSH receptors increased in both groups. The rate of increase, however, was more rapid in group B than in group A. The levels were significantly higher in group B than A at 3, 6, 9, and 12 months after delivery. Serum T4 and TBG concentrations decreased after delivery in both groups. Serum concentrations of T4 increased after delivery in group B but not in group A. The concentration of T4 was significantly higher in group B than in group A at 9 and 12 months after delivery. Postpartum recurrence of hyperthyroidism was 5.0% in group A and 31.6% in group B, respectively, during the first year after delivery. These results suggest that administration of T4 during pregnancy and after delivery is effective in decreasing the level of antibodies to TSH receptors and to prevent the postpartum recurrence of hyperthyroidism.