Thyroid disease in the perinatal period.

BACKGROUND Thyroid hormone plays a critical role in fetal development. In pregnancy, increased thyroid hormone synthesis is required to meet fetal needs, resulting in increased iodine requirements. OBJECTIVE This article outlines changes to thyroid physiology and iodine requirements in pregnancy, pregnancy specific reference ranges for thyroid function tests and detection and management of thyroid conditions in pregnancy. DISCUSSION Thyroid dysfunction affects 2-3% of pregnant women. Pregnancy specific reference ranges are required to define thyroid conditions in pregnancy and to guide treatment. Overt maternal hypothyroidism is associated with adverse pregnancy outcomes; thyroxine treatment should be commenced immediately in this condition. Thyroxine treatment has also been shown to be effective for pregnant women with subclinical hypothyroidism who are thyroid peroxidase antibody positive. Gestational thyrotoxicosis needs to be differentiated from Graves disease and rarely requires thionamide treatment. Postpartum thyroiditis most commonly presents with isolated hypothyroidism but a biphasic presentation and isolated hyperthyroidism can occur: a high index of suspicion is warranted for diagnosis.