1. Hypothyroidism in either the mother or the fetus can have serious adverse consequences for the fetus and must therefore be avoided in the mother. Screening of the target patient population is recommended at the first prenatal follow-up visit or at the time of confirmation of pregnancy. 2. If hypothyroidism has been diagnosed prior to pregnancy, the dose of levothyroxine (L-T4) needs to be adjusted to a TSH no higher than 2.5 mU/L prior to pregnancy. 3. The dose of levothyroxine (L-T4) usually needs to be increased by 30-50% at 4-6 weeks of gestation. The dose of levothyroxine (L-T4) depends on rapidly achieving or maintaining a serum TSH concentration of less than 2.5 mU/L in early pregnancy (first trimester) and less than 3.0 mU/L in April through June and July through mid-September. thyroid function must be measured every 30-40 days. 5. Women with autoimmune thyroiditis (Hashimoto’s thyroiditis) who have normal thyroid function in early pregnancy are at higher risk of hypothyroidism and need to be monitored for TSH values. 6. Subclinical hypothyroidism (serum TSH concentrations above the upper limit of normal with normal free thyroxine) has adverse effects on the mother and fetus, and treatment with levothyroxine (L-T4) improves the possible adverse consequences for the mother at delivery, but the effect on long-term fetal neurodevelopment is unclear. However, because the potential benefits outweigh the risks, levothyroxine (L-T4) replacement therapy is still recommended in women with subclinical hypothyroidism during pregnancy. 7. After delivery, the dose of levothyroxine (L-T4) needs to be adjusted downward in most hypothyroid patients compared to pregnancy.