Less thyroid hormone can impair the neurointellectual development of the offspring, while more may lead to miscarriage, gestational hypertension, preterm delivery, low birth weight babies, intrauterine growth restriction, stillbirth, thyroid crisis and maternal congestive heart failure-related. Women who already have hyperthyroidism should prepare for pregnancy after normal thyroid function, while patients with hyperthyroidism treated with thyroidectomy or 131I need to wait at least 6 months before pregnancy. Diagnosis 1. Serum TSH <0.1 mIU/L in T1 (0-12 weeks of pregnancy) suggests the possibility of thyrotoxicosis. FT4, TT3, thyroid stimulating hormone receptor antibody (TRAb) and anti-thyroid peroxidase antibody (TPOAb) should be further determined. However, 131I uptake rates and radionuclide scans are contraindicated. 131I treatment is contraindicated to avoid the radiation effect of 131I on the fetus. 2. TSH <0.1miu ft4="">the upper limit of pregnancy-specific reference value, after excluding transient hyperthyroidism, can confirm the diagnosis of hyperthyroidism. 3. Transient hyperthyroidism usually returns to normal with serum FT4 on its own at 14-18 weeks of pregnancy. Anti-thyroid drug (ATD) therapy is not given. Etiology Graves’ disease accounts for 85% and transient hyperthyroidism for 10%. Treatment of patients with Graves’ disease before pregnancy 1. Patients with high titers of TRAb who plan to become pregnant within 2 years should opt for surgical removal of the thyroid gland. This is because TRAb maintains high titers for several months after the application of 131I treatment, which affects the quality of the fetus. 2. A pregnancy test is required 48h before 131I treatment to verify pregnancy to prevent the radiation effects of 131I on the fetus. 3. Pregnancy should not be allowed until 6 months after thyroid surgery or 131I treatment. Receive levothyroxine replacement therapy at this stage to maintain serum TSH at 0.3-2.5 mlU/L level. 4. Methimazole (MMI) has a risk of fetal malformation and it is recommended to discontinue MMI before pregnancy and switch to propylthiouracil (PTU). Treatment of hyperthyroidism in pregnancy 1. PTU therapy is preferred in T1 stage, and MMI is the second-line drug. 2. MMI is preferred in T2 stage (13-28 weeks of pregnancy) and T3 stage (after 28 weeks of pregnancy). 3. If surgical removal of thyroid gland is required, the best period is the second half of T2 stage. 4.FT4 is preferred as the monitoring index during the treatment period, and the control target is FT4 close to or mildly above the upper limit. For those who apply drug therapy, FT4 and TSH should be tested every 2-6 weeks. If you have Graves’ disease hyperthyroidism or a previous history of Graves’ disease, serum TRAb should be measured at 20-24 weeks of gestation. high titers reflect active Graves’ disease, which can increase the morbidity and mortality of fetal/neonatal hyperthyroidism if not diagnosed and treated in time.