In the clinical practice of doctors of absolutely any specialty, hypothyroidism remains relevant, since with a deficiency of thyroid hormones (TH), which are necessary for the normal functioning of almost every cell of the human body, severe changes develop in all organs and systems without exception. The role of thyroid hormones of the thyroid gland is especially great in the period of intrauterine and early postnatal life. During the period of intrauterine life, under the control of TH, the processes of embryogenesis are carried out, almost all organs and systems are differentiated and mature. TH has an exceptional effect on the formation and maturation of the brain. No other hormones have a similar effect. Deficiency of thyroid hormones leads to the fact that the brain stops in development, undergoes degenerative changes. It should be borne in mind that the principles of diagnosis and treatment of thyroid diseases in pregnant women differ significantly from the general principles. This is primarily due to the fact that during pregnancy there is a change in the metabolism of thyroid hormones and a dynamically changing interaction between the pituitary-thyroid systems of the mother and fetus.