Fetal hyperthyroidism: experience of treatment in four siblings.

The outcomes of four pregnancies in a woman previously made hypothyroid by partial thyroidectomy for hyperthyroidism are reported. During the first two pregnancies she had no antithyroid therapy; the first resulted in late intrauterine death of a fetus with features compatible with fetal hyperthyroidism and the second in a child with skull deformities probably due to uncontrolled fetal hyperthyroidism. During the third and fourth pregnancies the mother received carbimazole to control fetal hyperthyroidism; both babies were euthyroid at birth and thrived. In mothers at risk of having hyperthyroid infants the fetal heart rate should be measured routinely to enable hyperthyroidism to be diagnosed and treated in utero.