Reference values for thyroid function tests during pregnancy 1

Abstract

Euthyroid women experience dramatic changes in the demand for thyroid hormone production as early as the first trimester of pregnancy. These adaptations are important for fetal neurodevelopment and organ development as well as maternal health and successful full-term pregnancy. Thyroid disease is the most common endocrine condition in women of childbearing age and leads to complications in approximately 1–2% of all pregnancies. The hypermetabolic state of normal pregnancy makes clinical assessment of thyroid function more difficult and therefore thyroid function often needs to be investigated biochemically. However, physiological changes of pregnancy, including a 50% plasma volume expansion, increased thyroid binding globulin production, and a relative iodine deficiency, implicate that thyroid hormone reference ranges for non-pregnant women may not be appropriate in pregnancy. Therefore, gestation-specific reference intervals assist in appropriate clinical management of thyroid disease in pregnancy to ensure maternal and fetal health.