Reproductive Biology Insights

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.