Gastrointestinal malformations in two infants born to women with hyperthyroidism untreated in the first trimester.

We report two infants with gastrointestinal anomalies: one with esophageal atresia and tracheo-esophageal fistula and the other with biliary tree atresia, born to hyperthyroid women diagnosed and treated with methimazole after 14 weeks' gestation. Euthyroidism was documented in both infants. These cases raise the issue of whether untreated hyperthyroidism and not methimazole intake is the teratogen.