Perinatal Thyroid Dysfunction: Prenatal Diagnosis and Treatment.

Thyroid diseases affect up to 10% of women, but most respond well to treatment. During pregnancy, however, normal metabolic changes may obscure pathology, and improper management may harm the fetus. Tests for levels of thyroid stimulating hormone (TSH), free thyroxine, and free triiodothyronine are essential. Generally, high TSH values suggest primary hypothyroidism, while suppressed levels indicate hyperthyroidism. Hyperthyroidism is commonly manifested by goiter, ophthalmopathy, proximal muscle weakness, tachycardia, and weight loss or inability to gain weight. Among women, the most common etiology of thyroid disease is thyroid autoimmunity (Graves' disease or Hashimoto's thyroiditis); affected women are at an increased risk of postpartum thyroid dysfunction. Women who have Graves' disease diagnosed during pregnancy typically have a history of hyperthyroidism symptoms antedating conception, and occasionally thyroid stimulating immunoglobulins may be elevated enough to induce fetal hyperthyroidism. Women with Hashimoto's thyroiditis typically are euthyroid but may be hypothyroid with diffuse goiter; diagnosis is confirmed by elevated levels of antithyroid peroxidase antibodies or antimicrosomal antibodies. Other forms of thyroid dysfunction include benign or malignant nodules and hyperemesis gravidarum. Hypothyroidism typically is treated with levothyroxine. Hyperthyroidism is treated with antithyroid drugs. The goal is to avoid overdosage of medication, which could cause goiter and/or hypothyroidism in the fetus.