Among women with diminished ovarian reserve or unexplained infertility, low serum free triiodothyronine and thyroid peroxidase antibody positivity are associated with low antral follicle count, according to findings published in Thyroid.
“The considerable differences in the association of thyroid function on antral follicle count between women with a different underlying fertility problem warrant further research and indicate a different role for thyroid hormone on the ovary according to the pathophysiology of infertility,” Tim Korevaar, MD, PhD, of Erasmus University Medical Center in Rotterdam, the Netherlands, told Endocrine Today. “Second, specifically in women with unexplained infertility, our results may indicate that a too low or too high free T3 concentration could have a negative effect on oocyte development and maturation, which is in line with findings from experimental studies.”
Korevaar and colleagues analyzed data from 436 women aged 18 to 45 years seeking fertility treatment at Massachusetts General Hospital Fertility Center and not prescribed thyroid medication (mean age, 35 years; 83% white; 73% nonsmokers). Researchers measured thyroid function and antibodies, including serum thyroid peroxidase antibody (TPOAb) and serum thyroglobulin antibody (TgAb), as well as serum concentrations of menstrual cycle day 3 follicle-stimulating hormone (FSH) and ovarian antral follicle count, defined as the sum of antral follicles in both ovaries measured via transvaginal ultrasound on menstrual cycle day 3. Researchers sued multiple linear or mixed regression models to assess the association between thyroid function or autoimmunity with antral follicle count or day 3 FSH concentration.
Within the cohort, 5.6% had a thyroid-stimulating hormone level above the reference range (TSH > 4 mU/L), 10.6% has TPOAb positivity, 9.2% had TgAb positivity and 4.6% had positivity for both antibodies.
Researchers did not observe an association between thyroid function or TPOAb positivity with antral follicle count, but they observed an association between TgAb positivity and higher antral follicle count (mean difference, 3.4; 95% CI, 1.8-5.1).
In sensitivity analyses that included only women with diminished ovarian reserve or unexplained infertility, a lower free T3 level was associated with lower antral follicle count (P = .009) as was TPOAb positivity (P = .01), whereas TgAb positivity was not associated with antral follicle count, according to the researchers.
“This result is opposite to results from analyses performed in the whole population, suggesting that the association of TgAb positivity with [antral follicle count] differs between women depending on infertility diagnoses,” the researchers wrote.
Neither thyroid function nor thyroid antibody positivity status were associated with day 3 FSH concentration, according to researchers.
“If these results are replicated in the future, an optimal treatment aim could be identified toward which clinicians could strive when treating women with subclinical hypothyroidism,” Korevaar said. “These data should be replicated in an independent cohort and subanalyses of current, ongoing trials could also prove relevant with regards to the potential identification of an optimal treatment aim.” – by Regina Schaffer
Disclosures: The authors report no relevant financial disclosures.