I. Clinical hypothyroidism in pregnancy impairs the neurointellectual development of the offspring and increases the risk of preterm birth, miscarriage, low birth weight, stillbirth and gestational hypertension, and the evidence is positive that treatment must be given. The guidelines clearly recommend screening for all populations; emphasize that it is best to test for the 5 thyroid functions before pregnancy or at least during the 8th week of pregnancy (mainly for TSH, free T4 and TPOAb) and recommend the development of one’s own laboratory criteria; 2. Diagnostic criteria for hypothyroidism in pregnancy: it is recommended to establish criteria for early and middle and late pregnancy; T1 stage 1-12 weeks of gestation (early pregnancy), T2 stage 13-27 weeks of gestation (early gestation), and T2 stage 13-27 weeks of gestation (early gestation). T2 stage 13~27 weeks of gestation (mid pregnancy), T3 stage 28~40 weeks of gestation (late pregnancy). 3, clinical hypothyroidism in pregnancy diagnostic criteria: the establishment of TSH and FT4 reference values in pregnancy can be selected as 95% confidence interval, i.e. 2, 5th as the lower limit and 97, 5th as the upper limit. The diagnostic criteria for clinical hypothyroidism in pregnancy are: TSH > upper limit of reference value in pregnancy and FT4 < lower limit of reference value in pregnancy. 2011 version of ata guideline also suggests that women with t1 pregnancy with tsh > 10mIU/L can be diagnosed as clinical hypothyroidism with or without FT4 reduction. The therapeutic targets for serum TSH in clinical hypothyroidism in pregnancy are: 0,1~2,5 mIU/L in T1, 0,2~3,0 mIU/L in T2 and 0,3~3,0 mIU/L in T3. Once clinical hypothyroidism is identified, treatment should be started immediately to achieve the above therapeutic targets as soon as possible. The starting dose is 50-100ug/d, and the dose will be increased gradually according to the patient’s tolerance level; those with combined heart disease need to increase the dose slowly. In patients with severe clinical hypothyroidism, twice the replacement dose is given within a few days of starting treatment to normalize the extra-thyroidal T4 pool as soon as possible. Choose levothyroxine (L-T4) therapy for clinical hypothyroidism in pregnancy. Triiodothyronine (T3) or dry thyroid tablets are not given for treatment. 3. The dose of levothyroxine (L-T4) is reduced to pre-pregnancy level after delivery of clinical hypothyroidism, and the blood TSH level needs to be rechecked 6 weeks after delivery to adjust the dose of eugenol; 4. When is pregnancy suitable for patients with pre-pregnancy clinical hypothyroidism: it is recommended that TSH be controlled at early pregnancy level and stable for 3-6 months before pregnancy is recommended to start; II. Hypothyroidism (SCH) is a condition in which the maternal serum TSH level is above the upper limit of the pregnancy-specific reference value, while the FT4 level is within the pregnancy-specific reference value. The diagnostic criteria for subclinical hypothyroidism in pregnancy are: serum TSH > the upper limit of the pregnancy-specific reference value (97,5th) and serum FT4 within the reference value range (2,5th ~97,5th). The effect of subclinical hypothyroidism in pregnancy on fetal neurointellectual development is unclear. Those with subclinical hypothyroidism in pregnancy with positive TPOAb should receive L-T4 therapy. For pregnant women with TPOAb-negative subclinical hypothyroidism, this guideline neither opposes nor recommends L-T4 therapy. The starting dose of L-T4 can be selected according to the degree of TSH elevation; the starting dose of L-T4 is 50 μg/day for TSH > the upper pregnancy-specific reference value; the starting dose of L-T4 is 75 μg/day for TSH > 8,0 mIU/L; the dose of L-T4 is adjusted according to the therapeutic goal of TSH. . Isolated hypothyroxinemia refers to a pregnant woman with normal serum TSH levels and FT4 levels below the 5th or 10th percentile of the reference range. The reference value here refers to the gestation-specific FT4 reference value (2,5th to 97,5th). Serum FT4 levels below the 10th (P10) or 5th percentile (P5) of the pregnancy-specific reference values and normal serum TSH (2,5th to 97,5th of the pregnancy-specific reference values) are diagnostic of hypothyroxemia. Simple hypothyroxemia is defined as hypothyroxemia with negative autoantibodies to the thyroid gland. It is not known about the effect of simple hypothyroxemia on poor fetal development. So far, there are no reports of interventions for simple hypothyroxinemia. Therefore, there is a lack of evidence-based medicine for the treatment of simple hypothyroxinemia during pregnancy. There is insufficient evidence of increased adverse pregnancy outcomes and impaired neurointellectual development in the offspring in simple hypothyroxemia to recommend L-T4 therapy.