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Human Chorion Gonadotropin(hCG) shares a common alpha-subunit with Thyroid-stimulating hormone(TSH) and cross-reacts with the TSH receptor. TSH declines 1st trimester – nl = 0.03-2.0 mU/l. Estrogens increase Thyroid binding globulin (TBG), and Total Thyroxine and total triiodothyronine (TT4/TT3) increase with stable FT3/FT4. A radioactive iodine (RAI) scan is contraindicated during pregnancy
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Hajnáczky Károly (2025) studied this question.
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