Hypothyroidism detected in a pregnant woman at 12 weeks of pregnancy is necessary for supplemental treatment with levothyroxine sodium tablets, and whether or not there is any effect on the fetus will need to be determined by completing regular obstetric evaluations. Hypothyroidism detected at 12 weeks of pregnancy is also an option to continue the pregnancy, but levothyroxine sodium replacement therapy needs to be started immediately to control thyrotropin hormone in a reasonable range as soon as possible. The principle of treatment for hypothyroidism in pregnancy is to return the thyroid function to normal as soon as possible. The earlier the thyroid hormone reaches the standard, the less the impact of hypothyroidism on fetal brain development will be. Hypothyroidism in pregnancy will affect the neurointellectual development of the fetus, increase the risk of preterm labor, miscarriage, low-birth-weight babies, stillbirth, as well as gestational hypertension, gestational diabetes and so on. Therefore, whether hypothyroidism at 12 weeks of pregnancy has any adverse effect on the fetus requires completion of screening tests such as NT, followed by regular prenatal checkups and evaluation by the obstetrician to decide whether to continue the pregnancy.