When we talk about the causes of infertility, tubal disease, cervical disease, vaginal disease, ovarian disease, etc. always pop up in our mind, but we ignore the endocrine thyroid disease, which may also cause infertility. The main function of the thyroid gland is to synthesize and release thyroid hormones. The thyroid hormones secreted by the thyroid gland are involved in the metabolism of various substances in the body and have a direct impact on tissue differentiation, growth and development, and reproductive physiology, such as promoting the development and maturation of the gonads and maintaining normal testicular sperm production and menstrual function, all of which require the presence of normal thyroid function. Too much thyroid hormone can lead to hyperthyroidism. Under the effect of thyroid hormones, excessive estrogen is secreted and the endometrium proliferates, causing patients to have excessive and frequent menstruation and even dysfunctional uterine bleeding. As hyperthyroidism progresses, the secretion and metabolism of ovarian hormones are blocked, and the process of decomposition, inactivation and removal is accelerated, resulting in gradual degeneration and atrophy of the endometrium, leading to sporadic menstruation and reduced menstrual blood flow until amenorrhea. Insufficient synthesis and secretion of thyroid hormones can lead to hypothyroidism, which can also cause infertility, and may even cause lower heart rate, lipid disorders, constipation, and even problems with the heart, kidneys, and other organs. It is also not advisable for hypothyroid patients to become pregnant until their condition is fully controlled.