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.