Abstract
Background: Intravascular fetal transfusion is an important therapeutic advance but is associated with several complications. Regression of an umbilical artery associated with transfusion is rare. Case: A case of red blood cell alloimmunization managed by serial transfusions was complicated by functional loss of an umbilical artery during pregnancy. Refractory fetal bradycardia occurred during the last transfusion procedure, requiring emergency preterm cesarean delivery. Coagulative necrosis, thrombosis, and focal calcification of one umbilical artery was confirmed after delivery. Conclusion: Umbilical artery regression associated with transfusion therapy is rare and may complicate subsequent fetal transfusions.