RESUMEN
Twin gestations complicated by a single anomalus fetus present difficulties in obstetric management. It is unclear how the presence of a congenital anomaly in one twin affects its normal sibling. Parents may elect for obstetric management option such as expectant management or selective termination of the anomalous fetus in the hope maximizing the outcome for the normal co-twin. Thanatophoric dysplasia (TD) is the most common type of lethal skeletal dysplasia. Features of the disease are micromelic shortening of the limbs, relative macrocephaly with frontal bossing, flattened vertebrae, disorganized chondrocytes and trabeculae in the growth plates of the long bones, and shortened ribs resulting in a reduced thorax and a bell-shaped abdomen. We experienced a case of TD type I diagnosed in a dizygotic twins by ultrasound at 23 weeks' gestation and reported with concerned literatures.