What is a normal thyroid-stimulating hormone (TSH) level? Effects of stricter TSH thresholds on pregnancy outcomes after in vitro fertilization

Using a thyroid-stimulating hormone (TSH) cutoff of 2.5 mIU/L or 4.5 mIU/L, no differences in the rates of clinical pregnancy, delivery, or miscarriage were observed in this large, retrospective cohort study of first-cycle IVF patients from 2005 through 2008, after controlling for age. Although lowering the TSH threshold to 2.5 mIU/L would result in a nearly fivefold increase in the number of women being classified as hypothyroid, the lack of differences in maternal clinical outcomes must be considered in the current controversy regarding the relative merits of lowering the upper limit of normal of TSH. (Fertil Steril (R) 2010;94:2920-2. (c) 2010 by American Society for Reproductive Medicine.)