The umbilical cord usually has one vein and two arteries. The two arteries bring blood with dissolved nutrients and oxygen from the placenta to your baby and the vein brings waste products back to the placenta.
In about 1 in 100 babies, however, only one umbilical artery is present. In twins, it is more common and it is seen in about 5 in 100 babies.
A baby with only one artery will usually have a compensatory bigger sized artery, which will allow it to provide the needed blood flow throughout the pregnancy. In some cases, however, there may not be enough blood flow and this may affect its growth. Growth scans(ultrasounds) will therefore usually be done in the third trimester to ensure that your baby is growing well.
In some cases, a genetic defect may be present and there may be some cardiac, kidney or other organ malformations. A detailed anatomical ultrasound and a fetal cardiac echocardiogram are therefore usually recommended to evaluate these possibilities.
If an abnormality is found, the chance of a genetic defect being present is higher and genetic testing will often be recommended as well. It is reassuring to know that the majority of babies with a single umbilical artery are normal and do very well throughout the pregnancy and during labor and delivery.