1.Overview Permanent right umbilical vein): A transverse cut of both the gastric vesicle and umbilical vein is revealed in the fetal abdomen, the umbilical vein is turned to the left side of the fetus (pointing to the gastric vesicle), and the gallbladder is located to the left of the umbilical vein and to the right of the gastric vesicle, whereas normally the gallbladder should be located to the right of the umbilical vein. Most right umbilical veins can be connected to a venous duct in the liver, and the prognosis for this variant tends to be better. Very few right umbilical veins cross the liver and connect directly to the inferior vena cava or the right atrium, causing hemodynamic changes. This variant, often, can be combined with multiple malformations; therefore, the umbilical vein is found to be present, as the umbilical vein is carefully followed using CDFI for the presence of abnormal connections. 2.Pathophysiology Permanent right umbilical vein, also called persistent right umbilical vein, is only an anatomical variation rather than a fetal malformation, which means that the right umbilical vein that should have degenerated does not degenerate, while the left umbilical vein that should not have degenerated degenerates. The incidence is about 0.2% to 1%. At the end of embryonic week 4, the umbilical vein has two left and right veins and is directly connected to the venous sinus. Later, the umbilical vein anastomoses with the hepatic blood sinusoid and loses its connection to the venous sinusoid. The developmental growth of the fetal liver causes the umbilical veins in the liver to tangle, knot, and eventually degenerate. However, the left umbilical vein does not degenerate, but instead concentrates all the venous blood returning from the placenta to the fetus. When the left umbilical vein joins the left branch of the portal vein into the liver, some of the blood enters the right liver via the right branch of the portal vein and most of the blood flows back directly into the inferior vena cava and the right atrium via the venous catheter. If the right umbilical vein does not degenerate, instead the left umbilical vein degenerates, at that time, the right umbilical vein enters the liver and then enters the left hepatic lobe via the anastomotic branch. At the same time, it is directly connected to the venous catheter, thus creating a persistent right umbilical vein. The cause of this process is not known. In rare cases, the right umbilical vein may also cross the liver and connect directly to the inferior vena cava or the right atrium, causing hemodynamic abnormalities. The vast majority of persistent right umbilical veins are not associated with fetal anomalies, but only a few may be associated with fetal anomalies such as hydrocephalus, single umbilical artery, short limb, atrial septal defect, ventricular septal defect, aortic constriction, tracheoesophageal fistula, hypospadias, renal displacement, visceral inversion, abnormal bowel rotation, and anorectal malformation. If the right umbilical vein is directly connected to the inferior vena cava or the right atrium, or even the iliac vein, the sonogram does not show that the umbilical vein is connected to the venous catheter in the liver, so that the venous catheter is simply absent. Careful tracking of the umbilical vein can reveal abnormal connections, and ultrasound can help with the diagnosis. This condition can often be combined with multiple anomalies such as atrioventricular access, arrhythmias, single umbilical artery, hydronephrosis, renal agenesis, choroidal cysts, pleural effusion, hemiplegia, finger and toe anomalies, and even chromosomal abnormalities. Pure persistent right umbilical vein without other site anomalies is often a benign variant with a better prognosis. Once combined with other malformations, the prognosis often depends on the malformation. Therefore, ultrasound findings of persistent right umbilical vein should be followed by careful examination of the venous catheter to follow the course of the umbilical vein and venous catheter to see if it is connected to the inferior vena cava. Other areas should also be carefully examined. In cases of malformations, chromosomal examination is required, and if the karyotype is abnormal, the pregnancy should be terminated.