Transient neonatal hypothyroidism

Transient neonatal hypothyroidism is defined as a temporary abnormality of the thyroid function discovered at birth, which later reverts to a normal status. It may or may not require replacement therapy. Recovery to euthyroidism typically occurs in the first few months or years of life. Transient hypothyroidism is much more common in preterm infants but may occur in apparently healthy term infants. Causes of transient neonatal hypothyroidism include maternal and neonatal iodine deficiency or excess, drugs, intrauterine exposure to maternal antithyroid drugs, transplacental passage of maternal TSH receptor blocking antibodies, genetic mutations, prematurity, and congenital hemangioma/hemangioendothelioma. In many cases, an underlying etiology may not be determined. The diagnosis of transient hypothyroidism is not always possible at birth. In these cases, it is important to distinguish at some later point, with reevaluation of thyroid function, between permanent and transient congenital hypothyroidism.