Il umbilical cord it is a deciduous, therefore temporary, anatomical formation containing the blood vessels connecting the fetus to the placenta.
At birth, the umbilical cord or cord measures an average of 50-60 centimeters in length and 20 mm in diameter; the appearance is that of a twisted cord of mother-of-pearl colour, which reveals the dark shades of the blood contained in the vessels.
The knotty appearance of the umbilical cord is linked to the twisted course of its vessels and to the presence of swellings (the so-called false knots) in correspondence with the vascular loops.
What is the umbilical cord used for and how is it made?
The umbilical cord is the link between the placenta and the conceptus. Its presence allows the transfer of gases and other substances between mother and fetus, without there being a direct exchange between the blood of the two organisms. In this way, the so-called “placental barrier” can prevent the passage of many harmful substances, even if some can still cross it and harm the fetus.
As a rule, they run within the umbilical cord three blood vessels: the umbilical vein on one side and the two umbilical arteries, coiled around it, on the other. The latter, unlike those of the systemic circulation, carry venous blood, while blood rich in oxygen and nutrients flows in the umbilical vein.
Within the abdominal wall of the fetus, the umbilical vessels take different directions: the umbilical vein carries arterial blood to the heart, while the umbilical arteries surround the bladder and carry venous blood outward.
Outside the abdominal wall, along the funicular tract, these blood vessels go to the placental disc; from it, the umbilical vein receives oxygenated blood rich in nutrients, while the two umbilical arteries carry venous blood, poor in oxygen, but rich in carbon dioxide and other waste substances.
The fibers of the umbilical blood vessels are particularly rich in muscle cells; the physiological significance of this feature is inherent in the need to quickly stop the blood flow in case of rupture of the umbilical cord. Furthermore, the vessels are immersed in a mucous connective tissue (Warthon’s jelly), which surrounds and protects them, drawing nourishment through the interstitial route.
How is the umbilical cord formed?
The umbilical cord begins to take shape around the fifth week of gestation, replacing – from a functional point of view – the yolk sac, which guarantees nutritional supplies in the early stages of embryo development.
The yolk sac is initially connected to the chorion (membrane that encloses the embryo and puts it in relationship with the mother through the chorionic villi), but this relationship regresses with the development of the allantois, an extra-embryonic membrane that allows breathing, the nutrition and excretion of the embryo. It is precisely from the maturation of the allantois that the umbilical cord develops.
Diseases of the umbilical cord
The most frequent anomalies affecting the umbilical cord are those relating to its shape or length.
We talk about excessive length when the umbilical cord exceeds 80 cm at birth, and of absolute brevity when it does not reach 30 cm. There may also be one relative brevityin case the funicular section presents single or multiple turns around the neck or other parts of the fetal body.
In case of absolute brevity, the serious possibility that the cord breaks abruptly during labor must be considered. In the case of relative brevity, the danger is that the knots tighten further during labor, causing fetal distress.
And umbilical cord too thin it is associated with intrauterine growth retardation (IUGR) and hypotrophic placenta; moreover, due to the small amount of Warthon’s jelly, the folds of the funiculus can cause occlusive episodes, with more or less serious fetal asphyxia.
Normally the umbilical cord is inserted on the fetal side of the placenta, in a roughly central position. In about 10% of cases this insertion is marginal, while in about one case out of 100 the umbilical vessels run for a more or less long distance between the amnion and the chorion, before reaching the placental border (velamentous insertion). The lack of Warthon’s jelly in this tract exposes the vessels of the umbilical cord to a greater risk of dangerous injury during rupture of the membranes.
In true nodes – unlike the false ones, given by the physiological vascular loops – there is an effective knotting of the umbilical cord, with consequent strangulation – more or less serious – of the blood vessels that run through it.
True knots can tighten further during labor and cause fetal asphyxia.
Numerical abnormalities of the umbilical vessels
At birth, numerical abnormalities of the umbilical vessels may also be found; the most frequent one concerns the absence of one of the two umbilical arteries which, although rarely, can be associated with fetal alterations and chromosomal diseases.
Prolapse and prolapse
Two other possible complications concern procidentia and prolapse of the umbilical cord; they occur (see figure) when one or more loops of the funiculus appear in front of the part presented with membranes intact (procidentia) or broken (prolapse). In the latter case, in practice, the cord is expelled first and during delivery, the baby compresses it against the vaginal wall, blocking the flow of blood and oxygen.
Careful monitoring of the fetal heartbeat during labor allows you to detect any suffering of the baby and intervene promptly if circumstances require it; in this way the risks of severe complications linked to umbilical cord pathologies are minimized.
When the umbilical cord is cut, the newborn loses physiological contact with its mother, and then rediscovers it in her womb during breastfeeding.
Immediately after birth, the cord is cut about 10 cm away from the newborn’s abdomen, closing the residual stump with an elastic band or a plastic clip and wrapping it in dry sterile gauze. This maneuver favors the occlusion of the vessels, avoiding hemorrhages and infections. The umbilical cord does not contain sensitive nerve fibers, so the child does not feel any pain when cut.
The severed segment stuck to the baby’s abdomen slowly dries up. After cutting the cord, the umbilical vessels thrombose quickly and the stump, no longer supplied by the vessels, dries up, taking on a blackish-brown colour. This sort of appendix will be kept dry and clean, and covered with a sterile gauze to be changed several times a day, until, around the 5th-10th day of life, it detaches by itself.
The health personnel will give the nurse the necessary indications on the hygiene of the umbilical stump, suggesting – for example – that she wash her hands carefully before touching it, avoid covering it with the edge of the diaper, keep it dry and well ventilated during the day and avoid to detach it prematurely waiting for its spontaneous fall.
Infections of what remains of the umbilical cord are quite rare and can be heralded by symptoms such as purulent (pus) and foul-smelling discharge, redness and noticeable swelling.
Umbilical cord and stem cells
The blood of the umbilical cord is rich in hematopoietic stem cells, with potential use for transplantation purposes to treat rather serious blood diseases (currently the therapeutic applications are actually very limited). For this reason the umbilical cord and the placenta are no longer considered waste to be incinerated, but a precious resource to be kept for donations or for autologous use. On the basis of these considerations, in recent years real umbilical cord banks have arisen, in which the blood extracted from the placenta and from the cord at the time of delivery is kept; this is a particularly thriving business which, for the moment, is running much faster than concrete scientific progress on adult stem cells.