Twin fetal transfusion syndrome is a unique complication of monochorionic monozygotic twins with two amniotic sacs, where two fetuses are present in two separate amniotic sacs, but share a common placenta. Since the two fetuses share one placenta and there is a vascular anastomosis between the placentas, more and more serious complications can occur, such as the twin fetal transfusion syndrome. The specific pathogenesis is as follows: through the arteriovenous anastomosis between the placenta, blood is shunted from artery to vein in one direction, making one fetus the blood donor and the other the blood recipient, resulting in anemia and reduced blood volume in the blood donor, resulting in growth restriction, inadequate renal perfusion, low amniotic fluid and even death due to malnutrition; increased blood volume, increased arterial pressure, increased volume of organs and increased fetal weight in the blood recipient. In addition, it can cause congestive heart failure, fetal edema, and excessive amniotic fluid, which are life-threatening to both fetuses. In stage I, only the amount of amniotic fluid is abnormal, one is too much and the other is too little; in stage II, ultrasound cannot show the bladder of the donor; in stage III, there is abnormal blood flow in the umbilical artery, venous duct, and umbilical vein on dynamic ultrasound; in stage IV, there is edema or fluid in the abdominal cavity in either fetus; and in stage V, death of either fetus. Twin-birth transfusion syndrome is a serious threat to fetal life, and if left untreated, the fetal mortality rate is as high as 90%. Therefore, pregnant women, especially those with twin or multiple pregnancies, need to undergo regular obstetric examinations and ultrasound.