A twin pregnancy with a single chorionic villi and a single amniotic sac is a very high risk pregnancy in which a single fertilized egg divides and the two fetuses share a single amniotic cavity with no membranes separating the two fetuses. Therefore, in this case, the incidence of twin fetus transfusion syndrome, fetal arrest, umbilical cord entanglement and umbilical cord knotting, and fetal arrest are significantly more likely to occur. For pregnant women diagnosed with monochorionic monoamniotic twin fetuses, it is important to increase monitoring during pregnancy. If the fetus develops twin fetus transfusion syndrome or excessive amniotic fluid during pregnancy, it should be promptly hospitalized, and if necessary, the pregnancy should be reduced or terminated.