Thyroid Hormones, PCOS and the Reproductive System
Thyroid hormones have various effects on the reproductive system of the human female. Alteration in thyroid function, particularly hypothyroidism, can cause ovulatory dysfunction and lead to impaired female fertility. Hypothyroidism and PCOS are often accompanied by increased serum free testosterone, luteinizing hormone (LH) and high cholesterol. When the ovaries of hypothyroid women with PCOS are viewed with an ultrasound an increase in ovarian volume and the appearance of bilateral multicystic ovaries are often visible. When thyroid hormone replacement therapy is initiated, in addition to stabilizing thyroid hormone levels, ovarian cysts regress and ovarian volume is reduced.
Thyroid Hormone Replacement, Estradiol and the Androgens
In the current study a significant improvement in serum hormone levels occurred after thyroid hormone replacement therapy. Serum FT3 and FT4 levels increased whereas serum TSH, prolactin, estradiol, free testosterone and total testosterone levels decreased. The serum DHEAS levels of patients with polycystic ovaries remained high, and there was no overall change in serum cortisol, 17OHP and 11DOC levels. Improvement in the menstrual cycle occurred in 18 women. Serum total testosterone concentrations were significantly higher in hypothyroid patients without polycystic ovaries, and thyroid hormone replacement therapy achieved a significant reduction in total and free testosterone levels.
Thyroid Hormone Replacement and Menstrual Irregularities
Hypothyroid women commonly suffer from menstrual irregularities and impaired fertility attributed to annovulation and/or luteal phase defect. The present study showed that the women with hypothyroidism (with or without polycystic ovaries) had significantly larger ovaries when compared with controls, suggesting that thyroid dysfunction has a profound effect on ovarian size, and may also produce ovarian cysts.
Research in animals has shown that hypothyroidism causes collagen deposition within the ovarian intracellular matrix. In humans, hypothyroidism is characterized by deposition of mucopolysaccharides (hyaluronic acid and chondroitin sulfate) within the connective tissue of various organs. While additional collagen in the lips or to reduce the appearance of wrinkles can be a good thing, increased collagenic material in the ovaries creates problems with ovarian function and may dysregulate hormone synthesis.
Reproductive Hormone changes in Hypothyroid Women
The study showed that although the overall basal serum androgen level of patients with hypothyroidism tended to be higher, only the difference in total testosterone was statistically significant. Hypothyroid patients with polycystic ovaries had significantly higher serum DHEAS and free testosterone but lower androstenedione levels.
Achieving normal thyroid levels after replacement therapy decreased overall serum prolactin, E2, total and free T levels (but not androstenedione and DHEAS values) significantly compared to pre-treatment. Resumption of regular menses occurred in 50% of PCOS and 81% of non-PCOS patients after thyroid levels had been normalized. Additionally, the polycystic appearance of the ovaries disappeared in all patients after thyroxine treatment. These findings indicate that the PCOS-like appearance of the ovaries can be caused by primary hypothyroidism. A decrease in ovarian volume and resolution of ovarian cysts should be expected after euthyroidism has been achieved with thyroid hormone replacement therapy.