The incidence of this disease is 1 in 4,000 and the causes are thyroid dysgenesis (75%), thyroid hormone anomalies (10%), hypothalamic-pituitary TSH deficiency (5%), and transient hypothyroidism (10%). Transient hypothyroidism occurs due to drug-induced, high iodine and maternal thyroid-stimulating blocking antibodies (TSBAb) that pass through the placenta and suppress fetal thyroid function. Most cases are disseminated. Routine screening of newborns for hypothyroidism is practiced in developed countries and in China. The measurement of TSH in heel blood (test paper method) is currently considered to be the most reliable screening method. The criteria for suspicious cases is TSH 20-25 mU/L. For suspicious cases, serum TSH and T4 are further determined and the diagnostic criteria for this disease are: TSH >7 mU/L and TT4 <84 nmol/L (6.5 μg/dL) during 1-4 weeks of life. The specimen should be collected within 3-5 days after delivery. Collecting blood too early is influenced by the pulsatile secretion of TSH in the newborn and false positives occur. Screening too late delays the initiation of treatment and affects its effectiveness. The principle of treatment is early diagnosis and adequate treatment. The earlier thyroid hormone therapy is initiated, the better, and must be started within 4-6 weeks of delivery. Follow-up studies have found that if treatment is initiated within 45 days, the child's intelligence quotient (IQ) at 5-7 years of age is the same as that of a normal child, and that delaying treatment will affect the child's neurointellectual development. The treatment drug of choice is levothyroxine (L-T4). the starting dose of L-T4 is 10-15 μg/kg/day. The goal of treatment is to achieve a normal serum TT4 level as soon as possible and to maintain it in the upper 1/3 of the normal range for newborns, i.e. 10-16 μg/dL. To ensure the certainty of treatment, the FT4 should be measured again after the goal is achieved and maintained in the upper 1/3 of the normal range. Serum TSH values are generally not used as therapeutic target values. This is because increased TSH persists for a long time due to the time required for the adjustment of the hypothalamic-pituitary-thyroid axis. Treatment of transient neonatal hypothyroidism is usually maintained for 2-3 years, with discontinuation of medication depending on thyroid function. Those with developmental abnormalities require long-term medication.