High titer of thyrotropin-binding inhibitor immunoglobulin (TBII) in patients with Graves' disease can cause fetal hyperthyroidism during pregnancy. Prevention of fetal hyperthyroidism by administration of antithyroid drug (ATD) and levothyroxine (LT(4)) to pregnant patients who previously received ablative therapy has been reported. We administered iodine and LT(4) to a patient during gestation, because she had a severe adverse reaction to ATD. Although gestation proceeded normally, the infant showed transient neonatal hyperthyroidism right after birth. We believe that the fetus would have developed hyperthyroidism if we had not administered iodine to the mother. Administration of iodine and LT(4) to a pregnant patient with Graves' disease showing a high TBII after ablative therapy should be considered in rare patients with allergy to ATD.