Objective — to assess the compliance of a decrease in TSH in the first trimester of pregnancy with thyrotoxicosis syndrome. Material and methods. 92 pregnant women with diagnosed thyrotoxicosis without goiter and the presence of antibodies to tyroperoxidase participated in the cohort study. Pregnant women divided into two groups: with manifest thyrotoxicosis (n=38) and subclinical thyrotoxicosis (n=54). In the first group, clinical symptoms corresponding to thyrotoxicosis syndrome observed. In the second group, no clinical manifestations of thyrotoxicosis observed. Half of the pregnant women of the first group canceled with potassium iodide, the second half of the group continued to take potassium iodide. Against the background of cancellation of potassium iodide, severe hypothyroxinemia with relatively low TSH was observed, while in pregnant women who did not cancel potassium iodide, the thyroid status remained within the reference range. Discussion. The concept of «subclinical thyrotoxicosis» in pregnant women does not correspond to the presence of thyrotoxicosis syndrome, since HCG progressively increasing in the first trimester of pregnancy, performs the function of TSH. This situation should be regarded as a functional transient hypothyreotropinemia, which is the physiological state of pregnancy. Conclusion. Do not discontinue potassium iodide when hypothyrotropinemia in pregnant women; pregnancy management is carried out as physiological, according to the standards of pregnancy management.