Levothyroxine supplementation improves serum anti-Müllerian hormone levels in infertile patients with Hashimoto's thyroiditis.

Aim: Thyroid dysfunction and autoimmunity are associated with an adverse effect on fertility. An aberrant high thyroid stimulating hormone level is associated with diminished ovarian reserve in women of reproductive age; however, the utility of levothyroxine (LT4) replacement for infertile patients with subclinical hypothyroidism is still under discussion. The aim of this study was to investigate whether LT4 supplementation for infertile patients with subclinical hypothyroidism improves impaired ovarian function.

Methods: We measured levels of serum thyroid-related hormones and a biomarker of ovarian function, anti-Müllerian hormone (AMH) in infertile women from 2014 to 2015. Out of a consecutive 1431 infertile patients, 311 patients with an elevated thyroid stimulating hormone level (≥ 2.5 μIU/mL) underwent detailed thyroid examinations, including blood tests of thyroid antibodies. We recruited 174 infertile patients, excluding patients with factors impacting ovarian and thyroid function. We evaluated alterations in AMH and thyroid related hormone levels during LT4 supplementation and infertility treatment with assisted reproductive technology.

Results: After LT4 supplementation, no significant change in the average AMH level was detected overall. However, the AMH level in 35 patients with Hashimoto's disease increased significantly after treatment (1 month 1.3 ± 0.5 fold, P = 0.007; 3 months 1.3 ± 0.4 fold, P = 0.040). The AMH level in patients with thyroglobulin antibody-positive and thyroid peroxidase antibody-negative also significantly increased after LT4 treatment (1 and 3 months 1.5 fold; P = 0.023).

Conclusion: In the patients with Hashimoto's disease, preconception LT4 treatment may relieve adverse effects, including autoimmune antibodies, and support follicular development.