Clinical hypothyroidism during pregnancy impairs the neurointellectual development of the offspring and increases the risk of preterm birth, miscarriage, low birth weight, stillbirth and gestational hypertension, which must be treated. The first trimester of pregnancy, in particular, is a critical period for fetal neurological development, and medication needs to be administered as soon as possible to achieve the standard as soon as possible. Planning a pregnancy Women with clinical hypothyroidism who are planning a pregnancy need replacement therapy to restore thyroid hormone levels to normal. The specific treatment goals are: serum TSH 0. 1 – 2. 5 mIU/L, and ideally, TSH 0. 1 – 1. 5 mIU/L. Unplanned pregnancy in hypothyroid women The maternal requirement for thyroid hormone increases from the 4th to the 6th week of gestation, and then gradually increases until a steady state is reached at the 20th week of gestation and is maintained until delivery. Therefore, once pregnancy is detected, hypothyroid women on treatment need to increase their dosage as soon as possible according to their current condition and adjust the dosage according to TSH results. The goals of clinical hypothyroidism treatment during pregnancy, levothyroxine for clinical hypothyroidism during pregnancy, TSH goals are: T1 stage 0. 1 ~ 2. 5 mIU / L, T2 stage 0. 2 ~ 3. 0 mIU / L, T3 stage 0. 3 ~ 3. 0 mIU / L. Once clinical hypothyroidism is identified, start treatment immediately to achieve the above treatment goals as soon as possible. Thyroid function should be monitored every 4 weeks during the first half of pregnancy (1-20 weeks) in women with clinical hypothyroidism. Serum thyroid function should be measured once between 26 and 32 weeks of gestation. Postpartum clinical hypothyroidism in pregnancy The increased demand for thyroid hormones in clinical hypothyroidism in pregnancy is due to the pregnancy itself. Therefore, the postpartum LT4 dose should be reduced accordingly and maternal serum TSH levels should be rechecked at 6 weeks postpartum. The recommended choice of thyroid hormone replacement during pregnancy is LT4 (Euthyrox or Raltez), but not thyroid tablets, because thyroid tablets are dried and ground thyroid gland from animals, and firstly, their thyroid hormone content is unstable, and secondly, they contain both T4 and T3, and their ratio is not consistent with human needs, as the T3 content is much higher than that required by the human body.