Some mothers-to-be have unexpectedly found that their thyroid hormone levels have risen during their maternity checkups. In order to help patients find the answer, we interviewed Professor Ma from the Department of Gynecology of Peking Union Medical College Hospital, who has extensive clinical experience in perinatal care, obstetric complications and complications, as well as critical care and obstetric health education. Professor Ma first told the mothers-to-be that if they are sure that they do not have a history of hyperthyroidism before pregnancy, there is no need to be too alarmed if they find elevated thyroid hormones in early pregnancy. You should not be unfamiliar 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 and true hyperthyroidism? Prof. Ma said that transient hyperthyroidism in pregnancy can be characterized by severe nausea, vomiting, weight loss, and in severe cases, dehydration and ketosis (prolonged starvation leads to a serious lack of energy intake, and 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 there are no 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 most patients do not need to take antithyroid drugs. 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.