Hyperthyroidism in pregnancy can occur for a variety of reasons, the most common being hyperthyroidism in pregnancy syndrome and Graves’ disease. Graves’ disease, also known as hyperthyroidism, is caused by an autoimmune disorder of the thyroid gland. Other rare causes of hyperthyroidism during pregnancy include transient hyperthyroidism due to Hashimoto’s thyroiditis, toxic multinodular goiter, and toxic adenoma. Because of the potential risks to both the pregnant woman and the fetus, hyperthyroidism during pregnancy can cause miscarriage, thyroid crisis, pre-eclampsia, heart failure, and abruptio placenta. It can also cause intrauterine growth retardation, premature birth, stillbirth and congenital malformation. Therefore, for hyperthyroidism in pregnancy, pregnant women and their families need to pay attention to the following points before they plan to get pregnant: 1. Hyperthyroidism, when is the most appropriate time to get pregnant? Female patients who have been clearly diagnosed with hyperthyroidism must inform their physicians in advance if they intend to have a child in the near future, and their doctors will adjust the treatment plan according to your specific situation. Generally speaking, if you were previously taking methimazole to treat hyperthyroidism, you will need to switch your medication to propylthiouracil. Since methimazole and propylthiouracil do not have the same efficacy, thyroid function may fluctuate after the switch, so you must wait until thyroid function is stable before considering pregnancy after switching to propylthiouracil. Some patients with hyperthyroidism are concerned about the adverse effects of anti-hyperthyroidism medication on pregnancy, so they often take it upon themselves to stop using propylthiouracil. This is very harmful. If the hyperthyroidism has been stabilized by treatment and the doctor thinks it is possible to stop the medication, it is possible to stop the medication and get pregnant. If the thyroid function has normalized after treatment, but it is not advisable to stop the medication, do not stop the medication and get pregnant because the hyperthyroidism will be aggravated in this case, which will lead to the use of larger doses of propylthiouracil in early pregnancy, which will be detrimental to the pregnancy. Some patients with hyperthyroidism may have an unplanned pregnancy, or some may find out that they have hyperthyroidism only after they are pregnant. If the patient does not have serious hyperthyroidism complications or pregnancy complications such as thyroid crisis, but only simple hyperthyroidism, active medication should be given to control the hyperthyroidism and restore the thyroid function to normal as soon as possible, which is less harmful to the pregnant woman and the fetus. On the contrary, if the pregnant woman has serious complications, not terminating the pregnancy often endangers the life of the pregnant woman, so the pregnancy should be terminated as soon as possible and the hyperthyroidism should be treated actively to save the life of the pregnant woman. 2. Hyperthyroidism, is it true hyperthyroidism? Since the treatment of transient hyperthyroidism and true hyperthyroidism are completely different, it is important to clarify whether the thyroid hormones found after pregnancy, including increased FT3 and FT4 and decreased thyroid stimulating hormone (TSH), are transient hyperthyroidism or true hyperthyroidism with Graves’ disease. Transient hyperthyroidism found during pregnancy mostly occurs in early pregnancy and is caused by elevated hCG, often accompanied by pregnancy vomiting, and with the prolongation of pregnancy, thyroid function will gradually return to normal and no anti-hyperthyroid medication is needed. If the true hyperthyroidism of Graves’ disease is misdiagnosed as transient hyperthyroidism and not treated with medication, it will lead to aggravation of hyperthyroidism, which will eventually endanger the pregnant woman and the fetus. Therefore, when hyperthyroidism is detected after pregnancy, it is important to distinguish between transient hyperthyroidism and true hyperthyroidism. So, how can we distinguish between transient hyperthyroidism and true hyperthyroidism in clinical practice? Generally speaking, the severity of transient hyperthyroidism, i.e. hyperthyroidism during pregnancy, is closely related to hCG and can be relieved by the decrease of hCG; moreover, transient hyperthyroidism often does not have a history of autoimmune thyroid disease and is often negative for thyroid antibodies such as thyroid stimulating hormone receptor antibody (TRAb) and thyroid peroxidase antibody (TPOAb); the thyroid gland is usually not enlarged on physical examination and the thyroid gland is often not abnormal on ultrasonography. Most patients have severe nausea, vomiting and other gastrointestinal symptoms, and in severe cases, even dehydration and ketosis. In contrast, Graves’ disease hyperthyroidism is caused by autoimmune disorder of the thyroid gland, so its severity is not related to hCG but to the degree of autoimmune disorder of the thyroid gland, so there are often high titers of thyroid autoantibodies in the serum, especially TRAb; the thyroid gland is often enlarged, and sometimes vascular murmurs can be heard on the thyroid gland; if untreated, hyperthyroidism will If untreated, hyperthyroidism will gradually worsen with the prolongation of pregnancy and will not remit on its own; Graves’ disease hyperthyroidism usually does not cause severe vomiting, but common symptoms of hyperthyroidism such as panic, wasting and excessive sweating will occur. 3. Which treatment is the most appropriate for hyperthyroidism? The current treatment for hyperthyroidism consists of three main modalities, namely anti-thyroid medication, isotope iodine and surgery. For treatment of hyperthyroidism in pregnancy, it is currently considered that antithyroid medication is preferred. The two main antithyroid medications are methimazole and propylthiouracil. Methimazole has been reported to cause developmental malformations in the first trimester of pregnancy, while propylthiouracil has not been reported to cause developmental malformations, so propylthiouracil should be used in early pregnancy. Methimazole and propylthiouracil can be used in the second and third trimesters of pregnancy depending on the situation. A small number of pregnant women with hyperthyroidism may experience serious side effects such as severe liver damage, severe allergic reactions to medications, severe leukopenia, etc., or if medications are not effective, surgery may be an option. Surgery should be performed at the right time, usually in the middle of pregnancy, i.e., the fourth to sixth month of pregnancy. It is important to emphasize that isotopic iodine treatment is strictly prohibited for hyperthyroidism during pregnancy, because isotopic iodine can freely enter the fetus through the placenta, thus causing damage to the fetal thyroid gland and resulting in the development of fetal hypothyroidism. The dangers of fetal hypothyroidism are enormous, including affecting mental development, premature birth, and stillbirth. Therefore, hyperthyroidism during pregnancy should not be treated with isotope iodine. Some pregnant women have had isotope iodine treatment before pregnancy, so how long can pregnancy take? Nowadays, it is generally recommended that pregnancy should be considered at least six months after isotope iodine treatment, and if conditions allow, pregnancy can be considered one year later. Since there is a high possibility of hypothyroidism after isotope iodine treatment, patients with hyperthyroidism who have had isotope iodine treatment must monitor their thyroid function closely and treat hypothyroidism promptly if it is detected.