Symptoms of hypothyroidism during pregnancy are the same as during non-pregnancy and present as: weakness, chills, constipation and weight gain. Due to pregnancy, the associated hypothyroidism symptoms are easily overlooked. Most patients are asymptomatic. The severity of hypothyroidism in pregnancy, which may adversely affect both the mother and the fetus, depends on the severity of the abnormal hormone levels. The diagnosis of hypothyroidism in pregnancy is based on different TSH indicators depending on the week of pregnancy (>2.5 in early pregnancy and >3 in middle and late pregnancy), combined with reduced FT4 (lower than normal maternal values during the same period). Subclinical hypothyroidism is defined as increased TSH and normal FT4. The need to screen all asymptomatic pregnant women for early pregnancy nail function remains controversial. We recommend selective screening (Level of Evidence 2C) and recommend screening in the following groups: 1. iodine deficient areas 2. with symptoms of hypothyroidism 3. with a family history of thyroid disease 4. or with a history of TPO antibodies in the pregnant woman 5. history of type I diabetes 6. history of head and neck radiation therapy 7. history of recurrent miscarriage 8. morbid obesity or infertility If the above criteria are met, TSH screening is performed in early pregnancy If TSH is normal, no further testing is required If TSH > 2.5, FT4 levels are required If subclinical hypothyroidism is reached (i.e. TSH > 2.5 and FT4 is normal), TPO antibody levels. All patients with a symptomatic diagnosis of hypothyroidism during pregnancy (week-specific TSH abnormalities >2.5 in early pregnancy and >3 in mid- to late-pregnancy with reduced FT4) need to be treated with thyroxine. In patients with subclinical hypothyroidism (abnormal TSH, normal FT4), hormone replacement therapy is also used (Evidence level 2B). Moderate to severe hypothyroidism requires full dose replacement (1.6ug/kg/d). After initiation of treatment, TSH should be monitored every four weeks due to dose adjustment. In subclinical or symptomatic hypothyroidism, the physiological requirement of T4 increases with the gestational weeks. The dose of levothyroxine should be increased as soon as pregnancy is detected. The usual method of dose increase is to increase the dose from the original pre-pregnancy daily dose to nine times a week (doubling the dose two days a week). Once pregnancy is detected, TSH levels need to be tested immediately and then adjusted every four weeks, at least every three months, according to TSH levels. Monitor TSH levels every four weeks according to the standard values of week-specific TSH and use pharmacological control to control TSH within the normal range for the corresponding week of pregnancy Even if the thyroid function is normal, increased serum anti-TPO antibodies can increase the rate of miscarriage and preterm delivery, and although the need for hormone replacement in this group of patients is still controversial, some studies suggest that the use of levothyroxine can reduce the risk mentioned above.