ABSTRACT
Monochorionic twins with discordant karyotypes are rare and mostly caused by post-zygotic mitotic nondisjunction. A 32 year old nulliparous woman at 11 weeks of gestation with spontaneous twin pregnancy was referred to our hospital. An amniocentesis was performed in both amniotic sacs at 15 weeks of pregnancy. One fetus in monochorionic twin pregnancy was diagnosed with Turner syndrome with cystic hygroma, and the other fetus was normal. Because of high mortality rate in abnormal fetuses, the umbilical cord coagulation was performed using radiofrequency ablation to prevent the damage of co-twin that may be caused by the demise of one fetus. After delivery, chorionicity of placenta was ascertained by pathologic exam. Postnatal findings of physical exam, abdominal and brain sonography were normal in the surviving neonate.