During pregnancy, serum TBG concentration ______, total thyroid hormone levels are ______, and free thyroid hormone levels are ______.

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During pregnancy, serum TBG concentration increases almost twofold because estrogen increases hepatic TBG production and TBG sialylation.TBG sialylation refers to the addition of a sialic acid residue to TBG, resulting in decreased clearance of TBG.As a result, there is increased total T₄ and total T₃ in the blood stream, because there is more protein to bind the hormones.The free forms of these hormones, however, are not affected by the change in protein concentration and are the analytes of choice to evaluate thyroid hormone levels during pregnancy.

During Pregnancy, Serum TBG Concentration ______, Total Thyroid Hormone Levels