The umbilical cord is a tube-like structure that starts to form during the 5th week after conception, connecting the developing fetus to the placenta. It is also called a ‘supply line.’ It transports nutrients and oxygen to the fetus and carries out the removal of fetal waste products.
- 1 Structure of Umbilical Cord
- 2 Development of Umbilical Cord
- 3 Functions Of Umbilical Cord
- 4 Storage of Umbilical Cord
- 5 Abnormalities related to Umbilical Cord
- 6 Umbilical Cord Infections
Structure of Umbilical Cord
The umbilical cord also being called the ‘navel string’ or ‘birth cord,’ is a channel between the developing fetus and the placenta. During prenatal development, the umbilical cord is part of the fetus physiologically and genetically. In humans, it usually contains two arteries (the umbilical arteries) and one vein (the umbilical vein), buried inside the Wharton’s jelly.
The umbilical vein delivers a fetus with oxygenated, nutrient-rich blood from the placenta whereas the fetal heart pumps low oxygen-containing blood and nutrient-depleted blood through the umbilical arteries back to the placenta.
The umbilical cord comprises Wharton’s jelly which is a gelatinous substance made up of widely spaced elongated fibroblasts separated by a three-dimensional meshwork of collagen fibres in a matrix of mucopolysaccharides which is rich in hyaluronic acid, that protects the blood vessels from inside. These three vessels are one vein and two arteries.
This structure is coated by amniotic epithelium which is a simple squamous epithelium, and the conjunctive layer is observed close to the essential substance of the umbilical cord which is known as fetal mesenchyme; It is constituted of mesenchymal connective tissue with stellate cells along with amorphous ground substance which contains plentiful glycogen.
Development of Umbilical Cord
The umbilical cord develops from and comprises miscellanies of the yolk sac and allantois. The cord forms by the 5th week of development (Read more on- Zygote- Formation Of a New Being | Stages of Gestation), replacing the yolk sac which acts as a source of nutrients for the embryo. The cord is not connected to the mother’s circulatory system directly although it connects the placenta, which does the transfer of materials to and from the maternal blood without allowing direct mixing it.
The length of the umbilical cord is about 50 centimetres long and about 2 centimetres in diameter (full-term neonate). The diameter decreases swiftly within the placenta. The umbilical artery has two layers. An outer layer comprising of circularly arranged smooth muscle cells. An inner layer which has irregularly and loosely arranged cells entrenched in rich ground substance staining metachromatic.
The smooth muscle cells of the layer are not much differentiated and contain only a small number of myofilaments and thus doubtful to contribute actively to the process of post-natal closure. The blood flow through the umbilical cord is around 35 ml/min at 20 weeks, and 240 ml/min at 40 weeks of gestation. Adapting to the fetal weight, this corresponds to 115 ml/min/ kg at 20 weeks and 64 ml/min/ kg at 40 weeks.
Functions Of Umbilical Cord
The umbilical cord plays a vital role in the transport of maternal nutrients for the development of the fetus during gestation. Within the fetus, the umbilical vein goes towards the transverse fissure of the liver and happens to split into two. One of these branches joins with the hepatic portal vein which carries blood into the liver.
The second branch bypasses the liver flowing into the inferior vena cava, which carries blood towards the heart. The two umbilical arteries are formed by the hypogastric arteries which branch from the internal iliac arteries and pass on either side of the urinary bladder into the cord, completing the route back to the placenta.
Storage of Umbilical Cord
The blood within the umbilical cord is known as cord blood, and it is a rich and available source of primitive and undifferentiated stem cells. These cord blood cells can be used for bone marrow transplant purposes. Some parents choose to have this blood abstracted from the baby’s umbilical blood transfer through early cord clamping and cutting and process to freeze it for long-term storage at a cord blood bank.
Although this practice is controversial, with critics proclaiming that withdrawing the early cord blood at the time of birth lead to increase the likelihood of childhood disease because of the high volume of blood taken, i.e., an average of 101 ml, concerning the baby’s total supply, i.e., typically 125ml/kg.
Several abnormalities are associated with the umbilical cord. The cord can be too long or too short. It may connect inappropriately to the placenta or develop to be knotted or compressed. It can lead to problems during pregnancy or during labour and delivery process. In some cases, cord abnormalities are diagnosed before delivery through an ultrasound. However, they usually are not diagnosed until after delivery when the cord is inspected directly.
〉 Single Umbilical Artery
Around 1% of singleton and 5% of multiple pregnancies, i.e., twins, triplets or more, have an umbilical cord that contains only two blood vessels instead of three, i.e., one artery is missing. The cause of a single umbilical artery is not known. Babies with single umbilical artery may have a higher risk for birth defects such as heart defects, central nervous system defects, urinary-tract defects as well as chromosomal abnormalities.
When the single umbilical artery is diagnosed during a routine ultrasound, certain prenatal tests need to be carried out to rule out birth defects. These tests include a comprehensive ultrasound, amniocentesis and also echocardiography which is a special type of ultrasound to evaluate the fetal heart in some cases. Also, the ultrasound after birth is also recommended.
〉 Umbilical Cord Prolapse
Umbilical cord prolapse arises when the cord slips inside the vagina after the membranes, i.e., a bag of waters has been ruptured, before the baby slopes into the birth canal. This complication can be seen in about 1 in 300 births. The baby can lay pressure on the cord as he passes through the cervix and vagina during labor and delivery.
Putting pressure on the cord reduces blood flow from the placenta to the baby, reducing the baby’s oxygen supply. It can result in stillbirth unless the baby is delivered usually by cesarean section. Pressure on the cord must be released by lifting the presenting fetal part away from the cord during the preparation of the woman for the prompt cesarean delivery process.
The risk of umbilical cord prolapse increases if,
- The baby is in a foot-first position.
- The woman is in the pre-term labour phase the umbilical cord is way too long.
- There is a high amount of amniotic fluid.
- The woman is delivering twins through the vagina.
〉 Vasa Previa
Vasa Previa arises when one or more blood vessels from the umbilical cord or placenta bypass the cervix beneath the baby. The blood vessels that are unguarded by the Wharton’s jelly in the cord, sometimes tear away when the cervix dilates or when the membranes rupture. This results in life-threatening bleeding. Even if the blood vessels do not tear apart, the baby can suffer from a lack of oxygen because of pressure on the blood vessels.
When vasa previa is diagnosed unpredictably at delivery, more than half the affected babies are stillborn. Although, when vasa previa is diagnosed by ultrasound earlier, fetal deaths can be prevented by cesarean section. Pregnant women with vasa previa may have painless vaginal bleeding in the second or third trimester of pregnancy.
A pregnant woman can be at increased risk for vasa previa if.
- She has the umbilical cord inserts abnormally into the fetal membranes, rather than the center of the placenta
- She has placenta previa, i.e., a low-lying placenta which covers part or all of the cervix or other placental abnormalities
〉 Nuchal Cord
A nuchal cord is a condition when the umbilical cord is wrapped around the fetus’s neck. Symptoms in the baby after birth from a prior nuchal cord include face duskiness, facial petechia, and also bleeding in the whites of the optic area. Complications comprise meconium, respiratory discomfort, anemia, and stillbirth.
More the number of wraps, the higher is the risk. The diagnosis can be made by the decrease in the baby’s heart rate during delivery. Nuchal cords are examined by running the finger over the baby’s neck once the head has come out.
Ultrasound may examine the condition before the labor. If it is detected during delivery, doctors may try to unwrap the cord or if that is not possible the clamping and cutting of the cord can be carried out. Nuchal cords can arise in about a quarter of deliveries. The cause of a nuchal cord is usually due to an excessive fetal movement.
Other reasons for cords moving around the neck of a fetus or result of loose knots include:
- The umbilical cord is way too long
- A poor cord structure
- Excess of amniotic fluid
- Having twins, triplets or multiples
〉 Umbilical Cord Knots
In some conditions, babies are born with one or more knots in the umbilical cord. Some knots occur during delivery when a baby with a nuchal cord is taken out through the loop. Others occur during pregnancy when the baby moves around.
Knots frequently occur when the umbilical cord is way too long and also during the identical-twin pregnancies when these identical twins have a single amniotic sac, and the babies’ cords can be entangled.
When the one knot or more knots can be pulled tight, cutting off the oxygen supply, it can result in miscarriage or stillbirth. A tightening knot can cause the baby to have heart rate abnormalities during labor and delivery.
〉 Umbilical Cord Cyst
Umbilical cord cysts are generally out pockets in the cord. There are two types of cysts, true and false cysts. True cysts are lined with cells and mainly contain miscellanies of early embryonic structures. Whereas the false cysts are formed from local degeneration of Wharton’s jelly.
Both types of cysts are sometimes associated with birth defects that include chromosomal abnormalities, kidney defects, and abdominal defects. When a cord cyst is diagnosed during an ultrasound, the doctors may recommend additional tests, such as amniocentesis and a comprehensive ultrasound to rule out birth defects.
Umbilical Cord Infections
It is a rare condition of infection in the umbilicus or nearby tissues that take place mainly in the neonatal period. It is an absolute medical emergency that can swiftly progress to systemic infection and further into death. Early diagnosis and treatment are important to avoid the morbidity and mortality associated with it.
Directly after birth, umbilicus converts colonized with different types of bacteria. Gram-positive cocci can be present within hours, followed by many enteric microorganisms. Symptoms typically start at an average of 3 days after birth.
Risk factors for omphalitis can include:
- Low birth weight,
- Membranes getting prolong ruptured
- Maternal infection,
- Umbilical catheterization,
- Nonsterile delivery,
- Maternal infection,
- Prolong labour, and
- Incorrect cord care.
The umbilical cord stump dries and separates with 6-8 days, and the wound then gets lined by epithelium and later get healed within 12-15 days. During this, both skin and enteric bacteria can colonize the devitalized tissue of the stump and can lead to infection.
It is thus a polymicrobial infection, and the common pathogens are Staphylococcus aureus, Streptococcus pyogenes, and gram-negative bacteria such as Escherichia coli, Klebsiella pneumonia, and Proteus mirabilis. If maternal infection with chorioamnionitis is examined, anaerobic bacteria such as Bacteroides fragilis, Clostridium perfringens, and Clostridium tetani also lead to infection.
The infection is characterized by tenderness, erythema, and induration of the umbilicus and nearby tissues. Patients may also experience the purulent drainage or bleeding from the cord stump. Foul-smelling drainage usually is linked with the presence of anaerobic infection.
〉 Umbilical Granuloma
It is a very common umbilical abnormality in newborns. The granuloma seems like a ball of moist, red tissue on the bellybutton. They frequently occur in newborns once the stump of the umbilical cord is fallen off. Granuloma is a moist and red lump of tissue. Although additional symptoms may include:
- The sticky mucus
- Irritation of the skin nearby the navel
- They do not cause pain or discomfort usually but occasionally happen to be infected.
Symptoms may include:
- Discomfort on touching the navel
- Warmth reddened area
- Red streaks starting from the navel
- Pus draining out from granuloma
Following options are available for taking care of the condition:
- Applying silver nitrate solution topically can cause a granuloma to dry out, shrink in, and disappear further. It is the most common treatment in neonates.
- Liquid nitrogen causes the tissue to freeze and fall off.
- Doctors may tie the base of the granuloma with surgical thread which cuts off blood supply to the tissue resulting in it eventually falling off.
- Doctors can gently remove the tissue with a scalpel.
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