Control goals for hypothyroidism in pregnancy The Clinical Practice Guidelines for Thyroid Disorders in Pregnancy and the Postpartum Period, issued by the American Thyroid Association in 2011, recommend the criteria for hypothyroidism in pregnancy as TSH <2.5 mIU/L in early pregnancy and TSH <3.0 mIU/L in mid- to late-term pregnancy [1]. If the thyroid function of hypothyroid patients is controlled within normal limits throughout pregnancy, the pregnancy outcome is mostly good and the postnatal infant has no abnormal intelligence level. Diet Studies have shown that hypothyroidism in pregnancy is easily combined with abnormal glucose metabolism, hypertension, and anemia [3]. In addition to ensuring the nutritional intake during pregnancy, the nutritional care plan should be developed according to the principles of low fat, high protein, high vitamin, high fiber, low sodium, iodine intake of at least 200 μg/d (except for Hashimoto's thyroiditis causing hypothyroidism), and water intake of 2000-3000 mL/d diet. The diet should be easy to digest and absorb, promote chewing slowly, small amount and many meals, avoid diarrhea. Soy products and other protein-rich, eating soy foods does not affect the thyroid function of pregnant women. Iodine supplementation There is a close link between iodine nutrition and thyroid function in pregnant women. Studies have shown that even with only marginal iodine deficiency, pregnant women and their newborns exhibit a relative deficiency in thyroid function, and it is recommended to increase the iodine supply to high-risk groups (pregnant women and newborns) [5]. The World Health Organization recommends intensive iodine supplementation during pregnancy with a recommended iodine intake of 200 μg/day and encourages pregnant women to consume iodized salt, iodized foods and seafood with high iodine content such as nori and kelp. If necessary, take multiple trace element tablets to supplement iodine. Medications The thyroid hormone needed for fetal development before 20 weeks mainly comes from the mother. The goal of treatment for hypothyroidism in pregnancy is to ensure adequate supply of thyroid hormone during the first period of rapid fetal brain development, i.e., 4-6 months of gestation, so treatment must be initiated before the 4th month of gestation. The earlier the initiation, the better, and ideally the standard of serum TSH < 2.5 mIU/L should be achieved at the beginning of pregnancy. The most effective treatment for hypothyroidism in pregnancy is levothyroxine tablets (L-T4 trade name Eugenol) replacement therapy. Patients should be instructed to take the medication as prescribed, preferably on an empty stomach in the early morning, and L-T4 should be taken at least 2 h apart from iron, calcium, and vitamins to prevent them from forming compounds that could interfere with absorption [6]. The administration should start with a small dose and the dosage should be adjusted according to the TSH level in time to bring the TSH level up to the standard as early as possible. The dose of L-T4 during pregnancy usually needs to be increased, often by more than 30%-50% compared to the non-pregnant state. To ensure normal fetal development, hypothyroid pregnant women should monitor their thyroid function every 0.5-1 month in early pregnancy to ensure TSH <2.5 mIU/L, and every month in mid- to late-pregnancy to ensure TSH <3 mIU/L. Regular monitoring of fetal development should be done at the hospital, and fetal distress should be prevented in late pregnancy. If there is any abnormality, hospitalization should be done as soon as possible to prevent preterm delivery and spontaneous abortion. In conjunction with local conditions, it is best to screen pregnant women, especially those with risk factors for hypothyroidism, for thyroid screening before 8 weeks of gestation.