Effect of permanent right umbilical vein on the fetus

Permanent right umbilical vein is also called persistent right umbilical vein. This is a manifestation of fetal malformation. It means that the right umbilical vein that should have degenerated has not completely degenerated, or the left azygos vein that should not have degenerated has completely degenerated. This has a relatively large impact on the fetus. It can easily cause fetal malformations during the embryonic period, and can easily lead to fetal arrhythmias, hydronephrosis, etc.

What is the right umbilical vein

Persistent right umbilical vein: The transverse section of the gastric bubble and the umbilical vein are simultaneously visible in the fetal abdomen. The umbilical vein turns to the left side of the fetal body (towards the gastric bubble). The gallbladder is located on the left side of the umbilical vein and on the right side of the gastric bubble. Normally, the gallbladder should be located on the right side of the umbilical vein. Most cases of the right umbilical vein can be connected to the ductus venosus within the liver, and this variant often has a better prognosis. In very rare cases, the right umbilical vein passes over the liver and directly connects to the inferior vena cava or right atrium, causing hemodynamic changes. This variation is often accompanied by multiple malformations. Therefore, when the umbilical vein is found, CDFI is used to carefully track the umbilical vein to see if there is an abnormal connection.

The influence of right umbilical vein on fetus

Permanent right umbilical vein, also called persistent right umbilical vein, is just an anatomical variation rather than a fetal malformation. It means that the right umbilical vein, which should have degenerated, has not degenerated, while the left umbilical vein, which should not have degenerated, has degenerated. The incidence rate is approximately 0.2%~1%. By the end of the fourth week of the embryo, there are two umbilical veins, one on the left and one on the right, which are directly connected to the venous sinus. Later, the umbilical vein anastomoses with the hepatic sinusoids and loses its connection with the venous sinus. The growth and development of the fetal liver causes the umbilical veins in the liver to become entangled, knotted, 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 connects to the left branch of the portal vein and enters the liver, part of the blood enters the right liver through the right branch of the portal vein, and most of the blood returns directly to the inferior vena cava and right atrium through the ductus venosus. If the right umbilical vein does not degenerate, but the left umbilical vein degenerates, at this time, the right umbilical vein enters the liver and then enters the left liver lobe through the anastomotic branch. At the same time, it is directly connected to the ductus venosus, thus forming a persistent right umbilical vein. The reasons for this process are unclear. In rare cases, the right umbilical vein may pass through the liver and directly connect to the inferior vena cava or right atrium, causing hemodynamic abnormalities.

The vast majority of persistent right umbilical vein malformations are not associated with fetal malformations, and only a few may be associated with fetal malformations, such as hydrocephalus, single umbilical artery, short limbs, atrial septal defect, ventricular septal defect, aortic coarctation, tracheoesophageal fistula, hypospadias, renal displacement, situs inversus, intestinal rotation abnormalities, and imperforate anus. If the right umbilical vein is directly connected to the inferior vena cava or right atrium, or even the iliac vein, the sonogram will not show that the umbilical vein is connected to the ductus venosus in the liver, and the ductus venosus is absent. Careful tracking of the umbilical vein can reveal abnormal connection sites, and color Doppler ultrasound can assist in diagnosis. This situation is often accompanied by multiple malformations, such as atrioventricular channel, arrhythmia, single umbilical artery, hydronephrosis, renal agenesis, choroidal cyst, pleural effusion, hemi-cone, finger and toe abnormalities, and even chromosomal malformations. Simple persistent right umbilical vein abnormalities without abnormalities in other parts are often benign variations, generally harmless, and have a good prognosis. Once combined with other deformities, the prognosis often depends on the degree of deformity. Therefore, if a persistent right umbilical vein is found on ultrasound, the ductus venosus should be carefully examined to track the direction of the umbilical vein and ductus venosus to understand whether they are connected to the inferior vena cava. Other parts should also be carefully checked. Those with deformities need to have their chromosomes checked, and if the karyotype is abnormal, the pregnancy should be terminated.

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