Impact of Controlled Ovarian Hyperstimulation on Thyroid Function

OBJECTIVE: To compare the effects of different protocols of controlled ovarian hyperstimulation on thyroid function with those of the natural menstrual cycle. STUDY DESIGN: Prospective controlled study. SETTING: University Medical Center. PATIENTS: A total of 97 women without a history of endocrine disease undergoing intrauterine insemination either in a natural cycle, or with mild ovarian hyperstimulation, or in vitro fertilization (IVF). MAIN OUTCOME MEASURES: estradiol (E2), thyroxine binding globulin (TBG), free thyroxine (FT4), total thyroxine (TT4) and thyroid stimulating hormone (TSH) during the midluteal phase. RESULTS: In the IVF group midluteal E2, TBG, and TT4 were significantly higher; midluteal FT4 was significantly lower (mean difference: -1.46 pmol/L; P < 0.001) and midluteal TSH was significantly higher (mean difference: 0.52 mU/L; P = 0.015). CONCLUSIONS: Ovarian hyperstimulation in IVF is associated with lower midluteal FT4. and higher midluteal TSH levels compared to the natural cycle.