Hypothyroidism in a breast-fed preterm infant resulting from maternal topical iodine exposure.

Hypothyroidism developed in a preterm infant, whose initial screening thyroid function test results were normal, at 2 weeks of life. The infant's mother was packing her Caesarian incision with iodine soaked gauze, resulting in a markedly increased breast milk iodine concentration. Treatment with oral L-thyroxine normalized thyroid function tests.