Which of the following is true regarding Umblical Cord
Ref. Gray’s anatomy.  41st edition. Page. 179
Umblical Cord: 

The umbilical cord forms around the fifth week of pregnancy and can grow up to 20 inches long at full-term.
Has two main layers: an outer layer of smooth muscle, and an inner layer containing a gelatinous fluid called Wharton's jelly.
Vasculature - one vein and two arteries. The vein carries oxygen and nutrient-rich blood from the placenta to the fetus, and the arteries carry deoxygenated and nutrient-depleted blood away from the fetus.

Clinical Anatomy:

Single umbilical artery: Related to congenital anamolies including problems with the heart, nervous system, chromosomes and urinary tract. This problem can be detected before birth.
Umbilical cord prolapse: Umbilical cord may prolapse, or slip into the birth canal, and become compressed during delivery, which can cut off the baby's blood supply
Umbilical cord knots: It is not uncommon for the cord to become wrapped around the baby's neck, but this rarely causes serious problems.
Umbilical cord cysts: Sometimes cysts can be seen developing on the umbilical cord via ultrasound. This can lead to abnormalities in the kidneys, chromosomes and abdomen.
Vasa previa: In rare cases, umbilical cord blood vessels may shift outside of the protection of the cord and move underneath the baby. This can lead to tears in the vessels and life-threatening bleeding. Pregnant women who experience bleeding in the second or third trimester should seek medical attention to rule out this complication.
One artery and two veins
Presence of one vein indicates congenital anomaly
Wharton jelly is the connective tissue of the cord
Two artery only