Subclinical Hypothyroidism and Normogonadotropic Anovulation

Thyroid hormones (TH) can modify the functioning of the hypothalamic-pituitary-ovarian axis, affecting the functions of granulosa cells and the development and apoptosis of preantral follicles. TH receptors are present within the oocytes, and TH and anti-thyroid antibodies (ATA) are present in the follicular fluid. Improper thyroid function can cause ovulation disorders, luteal phase failure, impaired endometrial receptivity and result in implantation failures and recurrent miscarriages. While overt hypothyroidism is treated to improve fertility, the effect of subclinical hypothyroidism (SCH) and the presence of circulating ATAs on fertility and obstetric outcomes is uncertain and data on ovarian reserve rates are conflicting. Among the causes of ovulation disorders (group II according to the WHO classification), polycystic ovary syndrome (PCOS) dominates, found in 3-15% of women of reproductive age, and the remaining group of causes is the so-called Hypothalamic-Pituitary-Ovarian Axis Dysfunction (HPOD). The exact etiology of both entities is unknown.