Hyperthyroidism and Pregnancy Hyperthyroidism in pregnancy includes hyperthyroidism diagnosed before pregnancy and hyperthyroidism first diagnosed during pregnancy. Chorionic gonadotropin (HCG)-associated hyperthyroidism, including transient hyperthyroidism in pregnancy (THHG), has a similar clinical presentation to hyperthyroidism and should be differentiated. The prevalence of hyperthyroidism in pregnancy is 0.1-0.2%. 95% of hyperthyroidism in pregnancy is due to Graves’ disease. The clinical pattern of hyperthyroidism during pregnancy is that the symptoms of hyperthyroidism increase in the first 5 months of pregnancy, decrease in the second 5 months, and increase again after delivery. 1. Effects of hyperthyroidism on pregnancy and fetus: The adverse effects of uncontrolled hyperthyroidism on pregnant women include miscarriage, preterm delivery, pre-eclampsia, congestive heart failure, hyperthyroid crisis, placental abruption and infection. The effects on the fetus include neonatal hyperthyroidism, intrauterine growth retardation, prematurity, small for full term (SGA), and stillbirth. Effective control of hyperthyroidism can significantly improve the outcome of pregnancy. 2. Clinical manifestations and diagnosis of hyperthyroidism in pregnancy: a distinction should be made between combined hyperthyroidism in pregnancy and HCG-associated hyperthyroidism. (1) Pregnancy-associated hyperthyroidism: the symptoms of hypermetabolism and physiological goiter during pregnancy are very similar to those of hyperthyroidism, and due to the increase in thyroxine-binding globulin (TBG) and the corresponding increase in blood TT3 and TT4, these make the diagnosis of hyperthyroidism difficult. Hyperthyroidism should be suspected if the weight of the pregnant woman does not increase with the number of months of pregnancy, if her limbs lose weight, and if her heart rate at rest is greater than 100 beats/min. Hyperthyroidism may be diagnosed if TSH is decreased and FT3 or FT4 is increased. If there is also infiltrative proptosis, diffuse goiter, thyroid area tremor or vascular murmur, and positive serum TSAb, the diagnosis of Graves’ disease is made. (2) Transient hyperthyroidism in pregnancy: It is a form of HCG-associated hyperthyroidism that occurs in early pregnancy with a prevalence of 1.5%. HCG peaks in the third trimester, and excess HCG can stimulate TSH receptors to produce hyperthyroidism in pregnancy. Transient hyperthyroidism in pregnancy is characterized by severe and prolonged nausea and vomiting, weight loss of 5% or more, severe dehydration and ketosis, and no positive thyroid signs. There is a decrease in serum TSH and an increase in FT3 or FT4. Serum HCG levels are increased and correlate with the extent of the disease, which helps to differentiate it from Graves’ disease in pregnancy. 3. Treatment monitoring: Anti-thyroid drugs are preferred for the treatment of hyperthyroidism in pregnancy. A few patients need to opt for surgical treatment, and radioactive iodine therapy is prohibited. (1) Anti-thyroid drug (ATD) therapy: The effect of anti-thyroid drugs on the fetus: It has been reported that the incidence of congenital malformations in the fetus is 2% to 6% in untreated hyperthyroidism, and 1% to 3% in ATD-treated pregnant women. There was no significant difference between propylthiouracil (PTU) and methimazole (tebuconazole, MMI). However, it has also been reported that MMI may lead to embryonic dysplasia, including dermal hypoplasia, posterior nostril atresia, tracheo-testicular leak, papillary hypoplasia, facial dysmorphism and psychomotor retardation. In view of this, PTU should be preferred for the treatment of hyperthyroidism in pregnancy. However, MMI is also not a contraindicated drug in pregnancy and may be used as a second-line option. Detection of hyperthyroidism in pregnancy: FT4 is used as an indicator of thyroid function to maintain FT4 in the upper 1/3 of the normal range. TSH levels should not be used as an indicator for 2 months before starting treatment because serum TSH levels can remain suppressed for several months after serum FT4 reaches normal. Normal TSH levels are an indicator of effective control of hyperthyroidism, at which point ATD should be reduced or discontinued. (2) Anti-thyroid medication and breastfeeding: PTU therapy is chosen, but the infant’s thyroid function should be tested. It is recommended that the mother should take the medication after breastfeeding and wait 3 to 4 hours before the next breastfeeding. (3) Surgery: The indications for surgery are: significant goiter that requires high doses of ATD to control, PTU doses greater than 300 mg/day; allergy to ATD; heavy psychological burden, excessive fear of side effects on the fetus or inability to take medication regularly as prescribed. Surgery should be performed in the 4th-6th month of pregnancy. Surgery in the third month of pregnancy is likely to cause miscarriage. (4) Radioactive iodine: Radioactive iodine treatment is contraindicated during pregnancy. Pregnancy should be avoided for 6 months after radioactive iodine treatment. (5) Other treatments: betablockers, which can cause spontaneous abortion, intrauterine growth retardation, prolonged labor, neonatal bradycardia, hypotension, hypoglycemia and hyperbilirubinemia; iodine, which can cause goiter and hypothyroidism in newborns and can only be used for a short period of time before thyroid surgery and during thyroid crisis resuscitation.