Thyroid hormones interact with reproductive hormones in women, estrogens and progesterone, to preserve normal function of the ovaries and maturation of the egg (oocyte).   Thyroid dysfunction has been shown to adversely affect fertility. The thyroid has an autoimmune function, which is linked to conception failure.  Immunologic factors are known to play an important role in the processes of fertilization, implantation and fetal development. In hyperthyroidism or hypothyroidism, the balance of reproductive hormones can be impaired resulting in thyroid-related fertility problems. Even though there is regular menstrual period, there may be lack of ovulation.

Hyperthyroidism can cause a woman to have difficulties in not only getting pregnant, but also staying pregnant.  If an affected individual experience unhealthy weight loss, this can hamper the chances of falling pregnant, as well. In hypothyroid women there could be infrequent and light menstrual bleeding, no menstrual cycles or irregular cycles due to problems with ovulation. Levels of prolactin, may increase and this inhibit ovulation. Hypothyroidism is also associated with an increased risk of polycystic ovarian disease (PCOS), a condition that causes cysts on the ovaries and prevents pregnancy.

Thyroid hormones, previously thought not to affect male, are now being seen as having an important role in sperm production. Hypothyroidism may result in a decrease in the sex hormone binding globulin (SHBG) levels and a decrease in total serum testosterone levels, as well as a decrease in the LH and the follicle stimulating hormone (FSH) levels. Hypothyroid function is often associated with reduced libido and erectile dysfunction; it also has an adverse effect on the form and structure of sperm – all of which can give rise to infertility in men. Hyperthyroidism is associated with elevated levels of testosterone, LH, and FSH. There are delays in Leydig cell development which affects spermatogenesis with resultant low sperm count and motility.

For full thyroid assessment you require hormone readings for TSH, T4, T3, rT3 & Thyroid Antibodies. Free T4, Free T3 and TRH may also be required. Certain thyroid blood tests, not routinely performed, are mandatory on all couples having infertility issues and on any woman who has had miscarriages. These tests are called anti-thyroid antibodies. When positive, these tests indicate that a person has an autoimmune condition known as Hashimoto’s thyroiditis. The tests may be positive in totally asymptomatic individuals; screening for thyroid insufficiency is indicated in women with ovulatory dysfunction.

Screening and treating of thyroid failure in infertile women can be beneficial in the following ways:

–         Potential reversal of infertility

–         Avoidance of expensive ART procedures

–         Avoiding the evolution to overt thyroid dysfunction in pregnancy

–         Avoiding the increased risk of miscarriage and postpartum thyroiditis and depression.

If overt thyroid dysfunction or sub-clinical hypothyroidism is detected, treatment is advised.