Thyroid Disease in Pregnancy and Postpartum

Pregnancy changes thyroid physiology before it changes the patient’s symptoms. Human chorionic gonadotropin (hCG) weakly stimulates the TSH receptor, so serum TSH commonly falls during the first trimester. Estrogen raises thyroxine-binding globulin, which raises total T4 and total T3 even when the patient is euthyroid. A nonpregnant laboratory range can therefore misclassify a pregnant patient. Interpret TSH using the laboratory’s population-specific, assay-specific trimester reference interval whenever one is available. If no pregnancy-specific interval exists, an upper first-trimester TSH reference limit near 4.00 µIU/mL is commonly used rather than applying the usual nonpregnant upper limit. Routine TSH screening of every pregnant patient is not recommended. Obtain targeted testing when risk is increased, including: - Prior thyroid disease, thyroid surgery, goiter, thyroid autoantibodies, or head and neck irradiation - Symptoms suggesting hypo- or hyperthyroidism - Type 1 diabetes or another autoimmune disease - Infertility, recurrent pregnancy loss, or a family history of thyroid disease - Exposure to medications that affect thyroid function, such as lithium or amiodarone A pregnant patient with fatigue, constipation, and mild weight change does not automatically have hypothyroidism;...