Thyroid Research Thyroid Research Archive Congenital

Hypothyroidism can occur in infants of mothers with hyperthyroidism caused by Graves’ disease during pregnancy

(March 2004)

The background of the study. Congenital hypothyroidism is usually caused by abnormal thyroid development, but it can be caused by thyrotropin (TSH) deficiency. The latter can be caused by suppression of TSH secretion by thyroxine (T4) in fetuses of mothers with hyperthyroidism caused by Graves’ disease. This study defined the clinical and biochemical abnormalities of infants with this type of congenital hypothyroidism.

How the study was done. Eighteen infants with hypothyroidism born to mothers with Graves’ hyperthyroidism who had not been treated or were inadequately treated during their pregnancies were identified through a newborn screening program. The diagnosis of TSH deficiency (pituitary hypothyroidism) in these infants was based on a low plasma free T4 concentration, a normal or low plasma TSH concentration, and the presence of Graves’ hyperthyroidism in the mother.

The results of the study. There were 12 girls and 6 boys; their gestational ages ranged from 35 to 41 weeks. Nine mothers were first found to have hyperthyroidism after delivery, usually after their infants were found to have hypothyroidism. Four mothers were found to have hyperthyroidism during the second or third trimester of pregnancy, and all had been treated with an antithyroid drug. Four mothers (one had a twin pregnancy) had hyperthyroidism and had been treated with an antithyroid drug before pregnancy, but only one was treated throughout pregnancy. Seventeen infants were treated with T4, and one infant became normal during evaluation and was not treated.

The conclusions of the study. Infants of mothers with hyperthyroidism caused by Graves’ disease may have hypothyroidism due to suppression of TSH secretion in the neonatal period, as a result of transfer of T4 from the mother in utero.

The original article. Kempers MJ, van Tijn DA, van Trotsenburg AS, de Vijlder JJ, Wiedijk BM, Vulsma T. Central congenital hypothyroidism due to gestational hyperthyroidism: detection where prevention failed. J Clin Endocrinol Metab 2003;88:5851-7.