Hypothyroidism during pregnancy occurs when there is an increase in TSH levels. If the T4 levels are low, it is considered overt hypothyroidism; if the T4 levels are normal, it is subclinical hypothyroidism. The most common cause of hypothyroidism during pregnancy is Hashimoto’s disease, characterized by anti-thyroid peroxidase antibodies. Pregnant women with a history of thyroid disease, type 1 diabetes, or those experiencing symptoms such as fatigue, constipation, cold intolerance, dry skin, hair loss, and weight gain should be evaluated for thyroid disease. Uncontrolled hypothyroidism can lead to various complications such as spontaneous abortion, preterm birth, preeclampsia, abruptio placentae, stillbirth, low birth weight, and impaired neuropsychological development of the newborn. Treatment with levothyroxine (LT4) should be initiated when TSH levels are above 4 mU/L at a dose of 1–2 µg/kg/day or 100 µg/day. Adjust the dose every 4 weeks to maintain TSH concentrations at or below 2.5 mU/L. No additional fetal surveillance during pregnancy is recommended. If a patient is being treated for hypothyroidism, consider increasing the LT4 dose by 25% upon pregnancy confirmation. During postpartum, decrease LT4 to pre-pregnancy level. If LT4 was started during pregnancy, maintain the exact dosage to prevent the disease progression and support lactation.