Perfil dos hormônios tireoidianos em mulheres durante o tratamento de reprodução assistida (fertilização in vitro) e a gestação

Abstract

Thyroid dysfunction is common among women of reproductive age and can affect fertility and pregnancy outcomes. The detectability of thyroid autoantibodies in this population had not been previously studied. Data on ovarian stimulation (OS) and in vitro fertilization (IVF) in the context of thyroid function are heterogeneous and inconsistent. This study aimed to assess whether thyroid function varies significantly during OS and IVF cycles involving frozen embryo transfer (FET) up to the end of the first trimester, and whether detectability—not just positivity—of thyroid autoantibodies correlates with ovarian reserve in women treated at a fertility clinic. We evaluated 453 women undergoing OS to investigate associations between thyroid autoantibodies and ovarian reserve, assessed via anti-Müllerian hormone (AMH) levels and antral follicle count (AFC). Anti-thyroid peroxidase antibody (TPOAb) and antithyroglobulin antibody (TgAb) were categorized as undetectable, minimally, moderately detectable, or positive. 24.4% of participants had at least one positive antibody. Most patients had detectable autoantibodies at low levels (42.3% for TPOAb and 66.9% for TgAb), but no statistically significant differences were found between antibody levels and ovarian reserve (AMH < or ≥ 1.1 ng/mL; AFC < or ≥ 7 follicles). TSH levels did not show correlation with ovarian reserve markers. In a prospective study, 275 euthyroid women were monitored for changes in TSH, free T4, and total T4 during OS, IVF, and early pregnancy. Participants received recombinant FSH/LH and progesterone for pituitary suppression, followed by GnRH agonist for final maturation and total embryo freezing. Thyroid function was assessed at seven time points, from OS initiation to 90 days post-embryo transfer. A transient TSH increase was observed after OS (1.47±0.47 to 1.82±0.79 mIU/L; p=0.001), peaking at pregnancy confirmation (1.86±0.74 mIU/L), with only 2.8% exceeding 4.0 mIU/L. Baseline and first-trimester TSH levels were similar (1.47±0.47 vs. 1.36±0.61 mIU/L; p=0.108). Free and total T4 levels did not correlate with TSH. Thyroid autoantibody prevalence was low—TPOAb (4.9%), TgAb (1.7%), both (2.9%)—with no significant effect on TSH or pregnancy outcomes. In conclusion, thyroid autoantibodies were not associated with ovarian reserve. Despite transient fluctuations in thyroid function during OS and early pregnancy, TSH levels did not demonstrate difference at the end of the first trimester compared to baseline. Given the TSH peak at pregnancy confirmation, TSH should be assessed before OS, at pregnancy confirmation in "freeze-all" cycles, and at the end of the first trimester.