- In a normal fetus, there is only one umbilical vein in the umbilical cord, which carries oxygenated blood and nutrient from the placenta to the fetus. On entering the front wall of the abdomen at the midline, the umbilical vein travels a short course towards the back and then turns towards the right side to form the portal sinus
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- Normal umbilical vein
- In a 4-week embryo, there are initially 2 umbilical veins but by 5th week of development, the entire right umbilical vein atrophies and disappears. The umbilical vein seen at the later gestation is originally the left umbilical vein;
Occasionally the right umbilical vein remains patent while the left umbilical vein has obliterated. This is called ‘persistent right umbilical vein’. Even more rarely, both umbilical veins are present;
- Persistent right umbilical vein occurs in 0.2% of the population. It is mostly an isolated condition and is not associated with any functional deficit after birth, as the umbilical vein will get obliterated following delivery anyway;
- Association with other abnormalities has been reported and they include
- Single umbilical artery
- Chromosomal abnormalities especially Edwards syndrome
- Structural malformation including cardiac, genitourinary and gastrointestinal system
- Genetic aberration
- Detailed fetal morphology scan is indicated for any ultrasound markers and structural abnormalities;
- For isolated persistent right umbilical vein (i.e. no other ultrasound markers for chromosomal abnormalities), antenatal screening with OSCAR or NIPT test is considered adequate. An amniocentesis is not advised, unless the couple wants a 100% certainty on the fetal karyotype.
