Maya KAKAGELDIYEVA
Hospital with a scientific and clinical center for physiology

Thyroid gland (TG) is normally the only source of thyroxine (T4), while about 80% of triiodothyronine (T3) is formed not in the thyroid gland, but by deiodination of T4 in peripheral tissues – muscles, liver, kidneys; the conversion of free T4 (FT4) into free T3 (FT3) occurs in the placenta [7, 8, 13, 16]. The optimal TSH level for planning pregnancy is 0,4-2,0 mU/l for hypothyroidism.