The umbilical cord is the baby's lifeline that connects the baby to the placenta. It carries oxygen and nutrients from the placenta to the baby through a single vein and waste products are taken from the baby back to the placenta via two arteries. Occasionally there is only one artery in the cord. This is known as a single umbilical artery, or SUA, and it affects between one in 100 and one in 500 pregnancies.
An SUA is more common in twin pregnancies, and where the umbilical cord attaches to the edge of the placenta, rather than in the middle. Often the number of vessels is not known until the placenta and membranes are examined after the baby is born, as counting the vessels in the cord is not a part of the routine scan in many hospitals.
If a single artery is seen in the cord at the 20 week scan, it is important to examine the baby's anatomy very carefully as there is an association with congenital abnormalities, particularly heart, skeletal, intestinal and kidney problems. SUA is also a marker for chromosomal abnormalities but as with all markers, if it is isolated, (if no other marker or abnormality is present), the baby is most likely to be normal.
A recent study found that all babies with chromosomal abnormalities had a structural abnormality as well as an SUA, and a round up of 37 studies over the past 40 years found that in an otherwise healthy infant, there is a slight increased risk of babies having kidney problems, but most of these were minor.
If other abnormalities were seen during your scan, you will probably have been offered amniocentesis to examine the baby's chromosomes.
If no abnormalities were seen during the scan, apart from the SUA, this should not cause any problems for you or your baby. Further scans may however be recommended to monitor your baby's growth as there is some evidence that babies with a single umbilical artery may grow at a slower rate.
I have no advice hun, but I wanted to give you a hug. I hope everything is ok 
