- In the umbilical cord, there are 2 umbilical arteries and one umbilical vein. The vein carries oxygenated blood and nutrition from the placenta to the baby and the arteries carry deoxygenated blood and metabolic waste from the baby back to the placenta;
- However, in some fetuses, there is only one umbilical artery and one umbilical vein. It is called ‘single umbilical artery (SUA)’, and sometimes it is labelled as ‘1A1V’;
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- umbilical cord (cross-sectional view)
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- Normal umbilical arteries
- SUA is present in 0.5% of fetuses and can be a normal variant;
- There is an association with other structural abnormalities in 40% of cases, with defects reported among urogenital, gastrointestinal, cardiovascular, respiratory and central nervous systems;
- There is also a weak association with chromosomal abnormalities especially Downs and Edwards syndromes;
- A detailed fetal morphology scan is advised for ultrasound markers and structural abnormalities;
- Invasive prenatal diagnosis is indicated if additional abnormalities are detected;
- For isolated SUA, 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 karyotyping;
- There is also a reported association with intrauterine growth restriction (~15%), hence follow-up scan for fetal growth is advised.
