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What is Physiologic Changes of the Thyroid metabolism during Pregnancy includes all except and explain in detail?
Pregnancy is a time of increased metabolic needs, and several factors in pregnancy also affect basic thyroid metabolism. hCG is secreted by the placenta, has significant homology with TSH, and is active at the TSH receptor. Pregnancy also results in elevated levels of serum TBG, requiring greater levels of total T4 and T3 to maintain adequate levels of free hormone. Overall, anticipated normal ranges of TSH concentration are lower during pregnancy with the lowest levels seen during the first trimester. Recommended ranges for TSH are 0.1 to 2.5 mIU/liter in the first trimester, 0.2 to 3.0 mIU/liter in the second trimester, and 0.3 to 3.0 mIU/liter in the third trimester.