Thyroid Disease in Pregnancy and Postpartum

Pregnancy changes thyroid laboratory values before it changes thyroid disease. Human chorionic gonadotropin (hCG) weakly stimulates the TSH receptor, so TSH commonly falls in early pregnancy. Estrogen increases thyroxine-binding globulin, which raises total T4 and total T3 even when the free, biologically active hormone concentration is appropriate. A non-pregnant reference interval can therefore label normal pregnancy physiology as disease—or miss disease by accepting a value that is abnormal for gestation. Interpret TSH using the laboratory’s population- and assay-specific trimester reference interval whenever available. If no local pregnancy interval is available, an upper TSH limit near 4.0 mIU/L has been used in the first trimester rather than the usual non-pregnant upper limit. Risk-based testing is used rather than universal TSH screening. Obtain thyroid testing when risk factors are present, including: - Previous thyroid disease, thyroid surgery, goitre, or thyroid autoantibodies - Symptoms suggestive of hypo- or hyperthyroidism - Type 1 diabetes or another autoimmune condition - Head or neck irradiation - Infertility or recurrent pregnancy loss - Family history of thyroid disease - Exposure to medications such as lithium or amiodarone...