An estimated 21 days after conception, the fetus begins to separate from the placenta by a connecting stalk. The stalk is the beginning of the umbilical cord and the early circulatory system. Approximately, five weeks after conception, the umbilical cord is almost completely formed with one stalk for waste (the early gastrointestinal track), two arteries and one vein. In the beginning, the two arteries send waste from the fetus to the placenta and the vein sends oxygenated blood and nutrients to the fetus from the placenta.
The role of the blood vessels changes throughout development. By week 10, the gastrointestinal track is formed as a natural protrusion from the umbilical cord. By the end of the third month, the gastrointestinal track has receded into the stomach. The cord reaches completion around the 28th week of pregnancy. It can reach up to 24 inches long. By approximately 31 weeks, it’s estimated that the umbilical cord carries 70 quarts of blood a day at a rate of four miles an hour, acting as an assistant pump to the heart.
The blood vessels that make up the umbilical cord can be in a variety of arrangements - twisted, straight, parallel or connected. They are embedded in Wharton’s Jelly, a durable liquid. Wharton’s jelly serves many purposes - it provides elasticity and cushioning, holds the vessels together, helps to deliver nutrients to the fetus, protects the life line, and contains the chemistry for the onset of labor. It also provides a natural clamping of the cord by collapsing structures in reaction to temperature changes. The Wharton’s jelly and the umbilical blood are rich sources of stem cells.
The umbilical cord can often be an indicator of fetal health and problems presented by the cord can be the cause of a number of defects. The cord can be too long or too short, might not connect properly, have a knot or be compressed. Most cord abnormalities are not found until after delivery but some can be seen on an ultrasound. All umbilical cords will exhibit unique properties, and differences do not necessarily equal an abnormality or have an impact on the fetus.
Approximately five percent of umbilical cords are either too short or too long. It’s relatively unknown what causes these differences, however, they’re often related to the movement of the fetus. Shorter cords are more common among multiples and longer cords are more common among male fetuses. Cord length has also been correlated with long-term consequences. Studies have associated lower IQ, motor skill abnormalities, and cerebral palsy with a shorter umbilical cord and longer cords have been linked to hyperactive behavior and problems with behavioral control. The cord can elongate until approximately 36 weeks gestation and the average length is 61cm or 24 inches. First pregnancies produce more short cords than subsequent ones. The diameter and circumference of the cord can also be relevant. The circumference range is from 3 cm-5cm. 3.7cm is considered average.
The umbilical cord naturally twists and more often to the left than to the right for unknown reasons. Twisting is related to fetal movement and excessive twisting can become dangerous for the fetus. In cases where the umbilical cord is too short, twisting is more likely to become dangerous. Less twisting than is normal can also mean possible problems because it indicates a lack of movement from the fetus.
The Wharton’s jelly is important for maintaining the integrity of the cord and resisting compression. When a cord twists or knots, it is most likely to do so where there is less Wharton’s jelly, because of the decreased resistance in those areas. It’s been reported that males have more Wharton’s jelly than females and that good nutrition can increase the amount present.
Cords without helices (there are usually about 10-11) can also be an indication of fetal health. The spiral shape is naturally formed by the growing blood vessels contained in the umbilical cord, but it’s unclear why this happens. Helices are formed as early as 42 days gestation and become fairly established by eight weeks gestation. The helices most often form in a counterclockwise direction, but sometimes they may exhibit two different directions.
Typically, the cord will insert into the center of the placenta and the blood vessels implant securely like the roots of a tree. In about 7% of singleton pregnancies, the cord will insert near the very end of the placenta. Rarely, there will be no umbilical cord at all and the fetus will be directly connected to the placenta. If the cord is short, then the further away the cord inserts from the cervix, the more likely a cesarean will be performed for delivery. In 1% of singleton pregnancies the cord will not insert into the placenta at all, instead the fetal vessels come through the external membranes before inserting into the placenta.
Cord prolapse occurs when the umbilical cord falls into the vagina after the bag of waters ruptures. When the baby descends into the birth canal, he or she can end up compressing the cord and cutting off blood supply and restricting oxygen. This is a fairly common complication, occurring once for every 300 pregnancies. The Wharton’s jelly present in the umbilical cord is very strong and can resist many incidences of compression, unfortunately though, it can often be underdeveloped in some places. The consequences of cord prolapse can be fatal for the baby, and a cesarean section is often necessary. However, it may resolve itself on its own. A health professional can reveal a cord prolapse by performing a pelvic examination and will be clued in by an abnormality in the fetal heartbeat once the bag of waters has ruptured. There are certain factors that can increase the incidence of cord prolapse: a breech position, preterm labor, longer than normal cord, too much amniotic fluid, rupturing the membranes to speed up labor, and delivery of twins vaginally.
25% of babies are born with a nuchal cord, where the cord is wrapped around the baby’s neck. This state rarely causes problems. Sometimes heart rate abnormalities will present themselves which indicates pressure on the cord, but rarely do these cause death or lasting effects. Cesarean delivery will be called for only occasionally. The cord can also be wrapped around a hand or foot, but again, this rarely causes problems.
There is still so much that the medical community does not know about functions and malfunctions of the umbilical cord. The amazing lifeline that supports the baby throughout pregnancy is a strong yet delicate structure. Ultrasound and Doppler techniques can be used to determine if problems are present. The visual image can often be sufficient in revealing abnormalities in the cord. In addition, the fetal blood flow through the umbilical cord can also be used as an indicator. The more forward blood flow from the fetus to the placenta through the cord, the healthier the fetus is determined to be. When viewing images of the umbilical cord, feel free to ask questions about any unique characteristics you may see. Identifying the state of the umbilical cord can be an important step towards delivering a healthy baby.
Have you seen you baby's umbilical cord on an ultrasound?
Photo Credit: Nevit DilmenUmbilical cord abnormalities [marchofdimes]
The Umbilical Cord [Yale]
Origin and Development of the Umbilical Cord [PregnancyInstitute]