The prevalence of hypothyroidism in women of childbearing age is 0.1-1%. Hypothyroidism is present in 5-6% of patients with unexplained infertility and anovulatory infertility, and in 2% of patients with tubal and male factors causing infertility. Hypothyroidism can lead to fertilization failure. It can lead to pregnancy complications such as embryonic abortion and growth restriction. Hypothyroidism also affects the neurological development of children. In contrast to natural pregnancies, IVF treatment requires ovulation treatment, which produces supraphysiologic amounts of estrogen, resulting in the production of large amounts of thyroid binding protein, which reduces the concentration of physiologically active free thyroxine and can lead to further exacerbation of hypothyroidism. Therefore, it is important to evaluate thyroid function in infertile patients undergoing in vitro fertilization.