Etiology Placenta umbilical factors 1)Obstructed of umbilical blood flow 2)Dysfunction of placenta 3)Fetal factors 4) Malformations of cardiovascular system 5)Intrauterine infectionPlacenta、umbilical factors 1) Obstructed of umbilical blood flow 2) Dysfunction of placenta 3) Fetal factors 4) Malformations of cardiovascular system 5) Intrauterine infection Etiology