Normal thyroid function is essential for normal function of the gonadal axis (control system that refers to the hypothalamus, pituitary gland, and gonadal glands; Pic. 4), thus important in maintaining normal reproductive capacity. On the contrary, any type of thyroid dysfunction may reduce the likelihood of pregnancy; the later can be restored to normal after appropriate treatment.
Thyroid diseases are very common in women of reproductive age. Infertility incidence is about 5-8% in women with hyperthyroidism. Previously menstrual disorders including particularly oligomenorrhea (infrequent menstruation) has been reported as 50% in people with hyperthyroidism. Hyperthyroidism may interfere with the mechanisms of ovulation and with sex hormone metabolism. If ovulation does not occur, the natural fertilization is not possible. If pregnancy does occur, the incidence of early pregnancy losses is increased and negatively affects fetal health.
With a proper treatment, the symptoms of hyperthyroidism including irregular periods are often cured.
Male fertility can be affected by a hyperthyroidism as well. It causes erectile dysfunction, delayed or premature ejaculation and low sex drive. Also, high thyroid levels can lead to higher than normal testosterone level and gonadotropin hormones. Steroid hormones, such as testosterone, are necessary for the development and maintenance of secondary sexual characteristics (features that appear during puberty) as well as initiation and maintenance of sperm development (spermatogenesis). Althought testosterone is required in large local concentrations to maintain the process, high testosterone levels in men may also lower the overall production of sperm. A failure spermatogenesis is a common cause of male infertility because a presence of abnormal sperm. The diagnosis of abnormal sperm does not mean infertility, but fertilization may take longer time. If natural conception does not work, there is always the option of in vitro fertilization (IVF).