Thyroid function during controlled ovarian hyperstimulation as part of in vitro fertilization.

ObjectiveTo determine the exact nature and timing of alterations in thyroid function throughout controlled ovarian hyperstimulation (COH).DesignProspective cohort study.SettingUniversity fertility clinic.Patient(s)Fifty-seven women undergoing COH as part of planned in vitro fertilization.Intervention(s)None.Main outcome measure(s)Timing and magnitude of change in serum thyroid hormones, including TSH, total and free T(4), E(2), and thyroxine-binding globulin (TBG), measured at six time points from before stimulation to 2 weeks after serum pregnancy test.Result(s)Geometric mean serum TSH increased during stimulation, peaking 1 week after hCG administration compared with baseline (2.44 vs. 1.42 mIU/L), as did free T(4) (1.52 vs. 1.38 ng/dL) and TBG (32.86 vs. 21.52 μg/mL). Estradiol levels increased, peaking at hCG administration (1743.21 vs. 71.37 pg/mL). Of 50 women with baseline TSH ≤ 2.5 mIU/L, 22 (44.0%) had a subsequent rise in TSH to >2.5 during or after COH. The pattern of change over time in TSH concentrations was significantly influenced by baseline hypothyroidism and whether pregnancy was achieved.Conclusion(s)COH led to significant elevations in TSH, often above pregnancy appropriate targets. These findings were particularly evident in women with preexisting hypothyroidism and may have important clinical implications for screening and thyroid hormone supplementation.