THYROID AND BRAIN DEVELOPMENT IN DEVELOPED AND DEVELOPING COUNTRIES

Maternal thyroid disorder, which is common, is linked with lowered intelligence in the child, and with neonatal encephalopathy, and cerebral palsy risk. Thyroid hormone is required in a wide range of developmental processes, and is necessary to healthy brain development. Even a relatively minor degree of maternal hypothyroxinemia during the first half of gestation is potentially dangerous for optimal fetal brain development.

In low resource countries, iodine deficiency in the pregnant woman can result in hypothyroxinemia and neurologic cretinism in the child. Supplying iodine before or early in pregnancy through provision of iodized salt or injection of iodinated oil can prevent neurologic catastrophe. However, iodization programs have been difficult to sustain long-term. Even in high resource countries, including the United States, optimal iodine nutrition in pregnancy remains a concern.

In high resource areas in which iodine status is adequate, the most common cause of thyroid deficiency is autoimmune thyroid disease. 1–2% of pregnant woman have frank hypothyroidism and receive replacement therapy, subclinical hypothyroidism is present in 2–3%, and about 10% of pregnant women have antithyroid antibodies which may, even in the absence of hypothyroidism, cause adverse outcome. Some antiepileptic medications can alter thyroid function. There is as yet no consensus concerning screening of women before or early in pregnancy for disordered thyroid function.

This presentation will review the evidence regarding thyroid hormone and thyroid autoimmunity, brain development, and outcome in the child.