Thyrotropin receptor antibodies in breast milk

Transient neonatal thyroid dysfunction is known to occur as a result of transplacental passage of maternal thyrotropin receptor antibodies (TRAbs). The presence of TRAbs in breast milk and its contribution to thyroid dysfunction in breast-fed infants has not been reported. We report the cases of two infants born to mothers with Graves' disease who were breast-fed. The mothers were treated with Propylthiouracil during pregnancy and after delivery. Thyroid function tests were obtained at periodic intervals in mothers and infants. TRAb levels were measured in the breast milk and in sera of mothers and infants. One infant developed hyperthyroidism. The other infant remained euthyroid. It was found that TRAb levels in breast milk were negligible in both cases and did not appear to contribute to thyroid dysfunction in the infants.