Decrease of free thyroxine levels after controlled ovarian hyperstimulation

Controlled ovarian hyperstimulation could lead to opposing effects on thyroid function. Therefore, in a prospective study of 65 women undergoing controlled ovarian hyperstimulation, thyroid hormones, T4-binding globulin, TPO antibodies, gonadotropins, estradiol, and PRL were measured before and after controlled ovarian hyperstimulation. After ovarian stimulation (mean +/- SE of mean): free T4 decreased, 14.4 +/- 0.2 vs. 12.9 +/- 0.2 pmol/L (P < 0.0001); thyroid-stimulating hormone increased, 2.3 +/- 0.3 vs. 3.0 +/- 0.4 mU/L (P < 0.0001); T4-binding globulin increased, 25.2 +/- 0.7 vs. 33.9 +/- 0.9 mg/L (P < 0.0001); total T4 increased, 98.1 +/- 2.3 vs. 114.6 +/- 2.5 nmol/L (P < 0.0001); total T3 increased, 2.0 +/- 0.04 vs. 2.3 +/- 0.07 nmol/L (P < 0.0001); TPO antibodies decreased, 370 +/- 233 U/mL vs. 355 +/- 224 U/mL (P < 0.0001); LH decreased, 8.1 +/- 1.1 vs. 0.4 +/-0.1 U/L (P < 0.0001); FSH did not change, 6.5 +/- 0.6 vs. 7.9 +/- 0.9 U/L (P = 0.08); human CG increased, <2 +/- 0.0 vs. 195 +/- 16 U/L (P < 0.0001); estradiol increased, 359.3 +/- 25.9 pmol/L vs. 3491.8 +/-298.3 pmol/L (P < 0.0001); and PRL increased, 0.23 +/- 0.02 vs. 0.95 +/- 0.06 U/L (P < 0.0001). Because low maternal free T4 and elevated maternal thyroid-stimulating hormone levels during early gestation have been reported to be associated with impaired psychomotor development in the offspring, our findings indicate the need for additional studies in the children of women who where exposed to high levels of estrogens around the time of conception.