Maternal hypothyroidism, thyroid antibody positivity, and hyperthyroidism may pose significant risks in terms of pregnancy complications and fetal adverse effects. Treatment of hyperthyroidism with thionamides remains the standard of care during pregnancy. Radioiodine use is contraindicated in pregnancy, including in the treatment of thyroid carcinoma, because of the risk of fetal hypothyroidism, subsequent cognitive impairment, and even fetal death. Normal thyroid function during pregnancy is essential to ensure delivery, to the best extent possible, of a healthy baby, which may be achieved with frequent monitoring of thyroid function during gestation and cautious adjustment of medications during treatment.