Impact of ovarian hyperstimulation on thyroid function in women with and without thyroid autoimmunity.

Pregnancy is accompanied by changes in thyroid function, but limited data are available on these changes in the very first weeks of pregnancy. Yet, T(4) plays a major role in implantation and early fetal development. We sought to determine thyroid function during this period and during the first trimester, in pregnancies achieved by assisted reproductive technology. Furthermore, the thyroid hormone profile was compared between euthyroid women with (TAI+) and without (TAI-) thyroid autoimmunity. We prospectively analyzed data from 35 women who received ovarian hyperstimulation (OH) and presented clinical pregnancies. The mean age of the women was 32 +/- 5 yr. Thyroid function tests [serum TSH and free T(4) (FT(4))] and thyroid antibody status were determined before OH (baseline values) and every 20 d after ovulation induction during the first trimester of pregnancy. Serum TSH and FT(4) increased significantly at d 20, compared with baseline values (3.3 +/- 2.4 vs. 1.8 +/- 0.9 mU/liter; P < 0.0001 and 13.2 +/- 1.7 vs. 12.4 +/- 1.9 ng/liter; P = 0.005). During the first trimester of pregnancy, there was a significant change over time for TSH and FT(4) (P < 0.001 and P = 0.005, respectively). Nine women (27%) were TAI+. The TSH curve among these TAI+ women was significantly higher compared with TAI- women (P = 0.010). The opposite was observed for the FT(4) curve (P = 0.020). In conclusion, the present study showed a significant increase of serum TSH and FT(4) levels after OH in the very first period of pregnancy compared with pre-OH levels and a significant impact of TAI on the thyroid hormone profile during the first trimester. This provides evidence for an altered thyroid function in euthyroid TAI+ patients.