Throughout pregnancy, the umbilical cord serves as the primary connection between mother and child. It provides the baby with oxygen and nourishment—it is, in a very literal sense, the baby’s lifeline. This means that if something goes wrong with the umbilical cord, it can sometimes become a medical emergency for which immediate medical attention must be sought. In this article we will discuss some of the abnormalities that can affect the umbilical cord.
Umbilical Cord Prolapse: an Obstetric Emergency
Under normal circumstances, the baby emerges from the birth canal trailing the umbilical cord behind it. In a small percentage of cases, however, the cord comes out first. This can happen if the amniotic sac has ruptured but the baby’s head is high in the pelvis; or perhaps the baby is not head down—for example, it may be in a breech or sideways position. When this occurs, as the fetus moves down into the pelvis, its weight puts pressure on the umbilical cord. This can cut off the fetal supply of blood and oxygen, creating a life-threatening situation. In most cases, delivery by immediate C-section is necessary.
One of the emergency measures that is taken when the cord prolapses is for the doctor (or sometimes a nurse) to insert his/her hand into the vagina to manually keep the cord away from the presenting (visible) part of the infant’s body until delivery is complete. This can lead to an emergency Cesarean section being done while underneath the surgical drape, and someone’s hand remains in the vagina until the baby is pulled out!
In rare cases—for example, if the baby is small or is in breech position—a doctor may be able to accomplish a vaginal delivery when there is a cord prolapse, but in cases like this, time is of the essence.
While umbilical cord prolapse happens only in 0.14 to 0.62 percent of births overall, the figure is closer to one percent for babies in the breech position, and it appears to happen to boys more often than girls. Statistics for cord prolapse appear to correlate with the incidence of multiple births, and in cases of twins, the second twin will more often be the one affected. The majority of negative outcomes occur in fetuses that are premature or suffer from congenital malformations, at least in hospital settings. Cord prolapse can be fatal to healthy, full-term infants if it occurs outside of a hospital, (e.g., during a planned home birth or in any other unorthodox birthing venue).
Other risk factors for umbilical cord prolapse include:
- Low birth weight
- Prematurity
- Transverse lie (baby’s spine perpendicular to mother’s) with back-up presentation, or breech presentation
- Premature labor with premature rupture of the membranes
- Abnormally long umbilical cord
- Polyhydramnios (an excessive amount of fluid in the amniotic sac)
- Artificial rupture of the membranes by a healthcare provider can lead to iatrogenic (caused by the doctor) cord prolapse if the water bag is intentionally broken during early labor and the baby’s head is not engaged.
Possible maternal complications resulting from umbilical cord prolapse include those caused by an emergency Cesarean Section, in which case sometimes due to the need for a very rapid surgery and delivery, certain steps of the surgery may not be done as gently as they normally would. There might be an increased risk of post-operative infection due to the presence of the cord in the vagina (which also contains bacteria) and there may not have been enough time for the mother to receive the usual dosage of pre-op antibiotics. The risk for the baby is much greater, however, and stillbirth is a possibility, as is damage from lack of oxygen if the cord compression lasts too long. However, most babies delivered promptly via C-section are born without complications.
Single Umbilical Artery
The umbilical cord is supposed to have two arteries and one vein, but in about 1 percent of pregnancies (and in 3 percent of pregnancies involving multiples), the cord only contains one artery. The arteries carry blood from the baby back to the placenta and tend to be very narrow vessels. The vein delivers blood from the mother to the baby, and the umbilical cord vein is a very large blood vessel, one of the largest veins in the human body!
The cause of this condition is unknown, but it can be detected with a routine ultrasound procedure. Some studies have suggested that a single umbilical artery puts the fetus at risk for certain birth defects, including abnormalities of the central nervous system, urinary tract, and heart, but only one cord artery is required for the fetus to live, and usually the baby is born without any other abnormalities.
Velamentous Insertion and Vasa Previa
The normal umbilical cord pathway is for the cord to exit the baby’s body and proceed right into the placenta, usually near the center. The location where the cord enters the placenta is called the cord insertion site.
A Velamentous cord insertion is when the umbilical cord blood vessels that connect the baby to the placenta have an abnormal pathway—they exit the baby’s body as usual, but as they head back toward the placenta, they exit the cord and enter the membranes on their way back to the placenta. Thus the cord insertion site becomes the amniotic membrane and not the placenta. This location makes the vessels vulnerable to tearing, since they lose the cushioning protection of the cord.
The worst-case scenario of this is vasa previa (not to be confused with placenta previa, which means the placenta is blocking the birth canal). Vasa previa means that there is a velamentous cord insertion and these fragile umbilical cord blood vessels (which are no longer protected by the cord itself) are travelling inside the amniotic membranes but are also covering the birth canal at the same time. The vessels are crossing the cervix underneath the fetus. During labor and particularly when the water bag breaks, these vessels can rupture, which can cause the baby to bleed to death. This is a difficult condition to diagnose prior to the onset of labor.
Nuchal cord
Approximately 25 percent of newborns have a nuchal cord—an umbilical cord that is wrapped around the infant’s neck. This may sound ominous, but most babies born this way are healthy, and these births are generally free of complications. Fetal monitoring may show periodic fetal heartbeat changes during labor, which may indicate that there is intermittent abnormal pressure on the umbilical cord, but this pressure is rarely great enough to cause serious problems, although a C-section delivery may be necessary in some cases. At every vaginal birth, as soon as the baby’s head emerges, the birth attendant performs a quick check of the neck area to “check for a cord.” If present, the cord is often gently pulled over the head, which is called “reducing” the cord.
Umbilical cord knots
In about 1 percent of births, the baby is born with a knot (or multiple knots) in the umbilical cord. These knots may form when the baby moves around in the womb during pregnancy, or they may form in cases of nuchal cord if the baby is pulled through the loop (“reducing” the cord) during the delivery. If the umbilical cord knot remains loose, there is generally no danger. If the knot is pulled tight during pregnancy, however, the baby’s oxygen may be cut off, which can result in stillbirth. C-section delivery is sometimes necessary in cases of knotted umbilical cord. Umbilical cord knots can occur if the umbilical cord is very long, or if the mother is carrying a rare type of identical twins called monoamniotic twins, who share the same amniotic sac (usually, even with identical twins, the babies have their own sacs).
Umbilical cord cyst
There are two types of umbilical cord cysts: True cysts and false cysts. A true umbilical cord cyst is lined with epithelial tissue and often contains remnants of embryonic formations. A false cyst, on the other hand, is a sac filled with fluid, and may be caused by swelling of the Wharton’s jelly, a gelatinous substance that lines the umbilical cord and is also found in the vitreous humor of the eye. Both types of cyst tend to accompany birth defects, so if an ultrasound detects an umbilical cord cyst, your doctor may want to conduct tests, including amniocentesis, or perhaps refer you to a specialist to ensure that your baby is free of birth defects.
Questions to Ask Your Doctor About Umbilical Cord Abnormalities
- In the event of an umbilical cord prolapse, will a vaginal birth be possible, or will I need a C-section?
- Can you tell whether umbilical cord knots have formed?
- If my baby’s umbilical cord is wrapped around his or her neck, is he or she in danger of choking?
- Is there a chance that my baby will suffer some sort of birth defect?