Acquired neonatal thyroid disease due to TSH receptor antibodies in breast milk

We investigated whether thyroid receptor antibodies (TRAb) could result in transient neonatal thyroid disease by transfer through milk from mothers treated for thyrotoxicosis.

To analyse whether breast milk content of TRAb in euthyroid mothers with treated thyrotoxicosis resulted in neonatal thyroid disease and whether extended breastfeeding prolonged the neonatal disease.

We tested three TRAb-positive mothers and the course, treatment and outcome for their offspring with neonatal thyrotoxicosis, and six healthy and two TRAb-negative euthyroid mothers with treated thyrotoxicosis during breastfeeding.

TRAb was analysed in serum and breast milk by a radioreceptor assay.

TRAb in serum was detectable in all treated mothers, in one mother during her four pregnancies, resulting in all neonates requiring treatment for thyrotoxicosis. Serum TRAb concentration in neonates decreased continuously with time after birth. Breast milk TRAb was detectable in all cases but not in the controls or in TRAb-negative mothers treated for thyrotoxicosis. The calculated half-life for offspring serum and breast milk TRAb was calculated as approx. 3 weeks and 2 months, respectively.

Euthyroid TRAb-positive mothers may cause transient neonatal thyroid disease which seems to be worse and more prolonged during breastfeeding as a consequence of TRAb in breast milk.