If you are sure that you do not have a history of hyperthyroidism before pregnancy, there is no need to be overly alarmed if you find elevated thyroid hormones in early pregnancy. You should be familiar with chorionic gonadotropin (hCG), but you may not know that hCG is structurally similar to thyroid stimulating hormone (TSH, which promotes thyroid secretion and plays an important role in the growth and metabolism of the thyroid gland itself), so hCG also has a certain role in promoting thyroid hormone secretion. In the third trimester, hCG secretion reaches its peak and stimulates the thyroid gland to secrete more thyroid hormone, which is called “transient hyperthyroidism in pregnancy”. How can we tell the difference between transient hyperthyroidism in pregnancy and true hyperthyroidism? Transient hyperthyroidism in pregnancy can be characterized by severe nausea, vomiting, weight loss, and in severe cases, dehydration and ketosis (prolonged starvation resulting in a severe lack of energy intake, the body mobilizes fat and protein hydrolysis to provide energy, resulting in an increase in acetone in the metabolites and a syndrome similar to diabetic ketosis), but without the typical symptoms of hyperthyroidism such as goiter and proptosis. The test is negative for thyroid excitatory antibodies (TRAb) and anti-thyroid peroxidase antibodies (TPOAb). In first-trimester hyperthyroidism in pregnancy, symptomatic treatment is the mainstay and anti-thyroid medication is not required. By the middle of pregnancy, the hCG level will gradually decrease and the thyroid hormones will slowly return to normal, and the clinical symptoms will disappear. However, thyroid stimulating hormone (TSH) returns to normal generally 1-2 months later than thyroid hormones (T4, T3). You may also be concerned that transient hyperthyroidism in pregnancy will not become true hyperthyroidism. In fact, most pregnant women have a peak in serum hCG that lasts only a few days and does not usually lead to hyperthyroidism. Most patients who are diagnosed with true hyperthyroidism after pregnancy often had hyperthyroidism before pregnancy but did not pay attention to it and only discovered it during maternity testing. Of course, pregnancy is also an autoimmune process, and hyperthyroidism may occur during pregnancy if fever, infection, insomnia, or intense mood swings occur, but pregnancy alone will not induce hyperthyroidism.