Aggravation of Thyrotoxicosis in Early Pregnancy and after Delivery in Graves' Disease*

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Abstract
The effect of pregnancy on the clinical course of Graves' disease was examined by studies on 41 pregnancies in 35 patients with Graves' disease, who were considered to be in a state of remission or near remission and were not receiving antithyroid drugs, during and after delivery. Eighteen of the 41 cases (44%) showed transient increases in the serum free T4 index (FT4 index) during weeks 10–15 of pregnancy, but normal thyroid function in the second and third trimesters. Similar transient increases in the serum free T3 index (FT3 index) were observed in early pregnancy in these patients. These early increases in the FT4 and FT3 indexes were specific to Graves' disease and were not observed in Hashimoto's disease. Two to 4 months postpartum, 32 cases (78%) developed various degrees of thyrotoxicosis, which was divided into 3 types: 1) persistent thyrotoxicosis with high radioactive iodine (RAIU) (10 cases), 2) transient thyrotoxicosis with normal or high RAIU) (10 cases), and 3) destruction-induced thyrotoxicosis with low RAIU (12 cases). An increase in the FT4 index in early pregnancy was significantly (P4 index during pregnancy.