The vein brings in oxygen and nutrients to the baby from the mother. The arteries are used to transport waste away from the baby to the mother via the placenta. The waste is then filtered through the maternal kidneys. The umbilical cord starts to form early in pregnancy, around the fifth week of gestation. It will get longer and take the famous coil shape as it does. The average length of an umbilical cord is about 22 to 24 inches.
Placental Exam and Umbilical Cord
If you are having a mid-pregnancy ultrasound, also known as a fetal anatomy survey, your ultrasonographer will examine the placenta. They are looking for many things. They will try to see both the arteries and veins during your exam. This is easier with color Doppler ultrasounds, but blood flow can be shown with your average ultrasound machine. The size and location of the placenta and umbilical cord will be noted.
Wharton’s Jelly and Knots
The Wharton’s Jelly is very thick and helps protect the arteries and veins from being compressed. The umbilical cord can loop around fetal parts and potentially knot in about 1% of all births. This is more common in identical twin pregnancies where one sac is shared or if your baby’s umbilical cord is longer than normal. Fetal monitoring might suggest significant cord compression, and at times, if the fetal heart pattern is concerning, a cesarean birth may be recommended.
Umbilical Cord Cysts
Umbilical cord cysts are found in less than 1% of cords. There are two main types: true cysts and false cysts. False cysts are related to the Wharton’s Jelly and filled with fluid. True cysts contain what’s leftover from the early parts of the pregnancy. Management of cysts depends on the type, size, location, gestational age at detection, and any associated anomalies. Most cysts resolve and do not predict poor outcome.
Single Umbilical Artery
About 1% of all babies will have a two-vessel umbilical cord, which is a single artery (single umbilical artery) rather than two. You will also see this in about 5% of pregnancies where there is more than one baby (twins, triplets, etc.). When this is found, a more detailed ultrasound is advised to check for other abnormalities and to follow fetal growth. About 20% of babies who only have one artery in the umbilical cord will have malformations.
Vasa Previa
This is where a blood vessel from the cord is not protected by the Wharton’s Jelly and actually crosses the cervix. This can lead to the tearing of the vessel during birth, dilation, or even simply pressure at the end of pregnancy. Early diagnosis via ultrasound is the key to a safe birth for this pregnancy. When diagnosed earlier in pregnancy, a cesarean is typically done around week 35 to prevent damage to the vessel. Typically, you may see painless bleeding in the second or third trimesters, or it is picked up at a routine ultrasound.
Velamentous Insertion
A velamentous insertion of the cord means that it inserts into the actual membranes rather than the center of the placenta. This leaves the vessels exposed in places, making it possible for them to become compressed as the baby gets bigger.
A Word From Verywell
The good news is that the vast majority of the time there are no complications with the umbilical cord. It is a fascinating structure that works with the placenta and baby.
