<prompt> Physiologic Changes of the Thyroid metabolism during Pregnancy includes all exceptIncreased levels of total T4 and T3Elevated levels of serum TBGhCG acts at TSH receptorTSH level is highest during the 1st trimester  <response>: 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 mIUliter in the first trimester, 0.2 to 3.0 mIUliter in the second trimester, and 0.3 to 3.0 mIUliter in the third trimester. 