Umbilical cord abnormalities
The umbilical cord begins to form at 5weeks after conception. It becomes progressively longer until 28 weeks of pregnancy, reaching an average length of 22 to 24 inches (1). As the cord gets longer, it generally coils around itself. The cord contains three blood vessels: two arteries and one vein.
- The vein carries oxygen and nutrients from the placenta (which connects to the mother's blood supply) to the baby.
- The two arteries transport waste from the baby to the placenta (where waste is transferred to the mother's blood and disposed of by her kidneys).
A gelatin-like tissue called Wharton's jelly cushions and protects these blood vessels.
A number of abnormalities can affect the umbilical cord. The cord may be too long or too short. It may connect improperly to the placenta or become knotted or compressed. Cord abnormalities can lead to problems during pregnancy or during labor and delivery.
In some cases, cord abnormalities are discovered before delivery during an ultrasound. However, they usually are not discovered until after delivery when the cord is examined directly. The following are the most frequent cord abnormalities and their possible effects on mother and baby.
What is single umbilical artery?
About 1 percent of singleton and about 5 percent of multiple pregnancies (twins, triplets or more) have an umbilical cord that contains only two blood vessels, instead of the normal three. In these cases, one artery is missing (2). The cause of this abnormality, called single umbilical artery, is unknown.
Studies suggest that babies with single umbilical artery have an increased risk for birth defects, including heart, central nervous system and urinary-tract defects and chromosomal abnormalities (2, 3). A woman whose baby is diagnosed with single umbilical artery during a routine ultrasound may be offered certain prenatal tests to diagnose or rule out birth defects. These tests may include a detailed ultrasound, amniocentesis (to check for chromosomal abnormalities) and in some cases, echocardiography (a special type of ultrasound to evaluate the fetal heart). The provider also may recommend that the baby have an ultrasound after birth.
What is umbilical cord prolapse?
Umbilical cord prolapse occurs when the cord slips into the vagina after the membranes (bag of waters) have ruptured, before the baby descends into the birth canal. This complication affects about 1 in 300 births (1). The baby can put pressure on the cord as he passes through the cervix and vagina during labor and delivery. Pressure on the cord reduces or cuts off blood flow from the placenta to the baby, decreasing the baby's oxygen supply. Umbilical cord prolapse can result in stillbirth unless the baby is delivered promptly, usually by cesarean section.
If the woman's membranes rupture and she feels something in her vagina, she should go to the hospital immediately or, in the United States, call 911. A health care provider may suspect umbilical cord prolapse if the bay develops heart rate abnormalities after the membranes have ruptured. The provider can confirm a cord prolapse by doing a pelvic examination. Cord prolapse is an emergency. Pressure on the cord must be relieved immediately by lifting the presenting fetal part away from the cord while preparing the woman for prompt cesarean delivery.
The risk of umbilical cord prolapse increases if:
- The baby is in a breech (foot-first) position.
- The woman is in preterm labor.
- The umbilical cord is too long.
- There is too much amniotic fluid.
- The provider ruptures the membranes to start or speed up labor.
- The woman is delivering twins vaginally. The second twin is more commonly affected.
What is vasa previa?
Vasa previa occurs when one or more blood vessels from the umbilical cord or placenta cross the cervix underneath the baby. The blood vessels, unprotected by the Wharton's jelly in the umbilical cord or the tissue in the placenta, sometimes tear when the cervix dilates or the membranes rupture. This can result in life-threatening bleeding in the baby. Even if the blood vessels do not tear, the baby may suffer from lack of oxygen due to pressure on the blood vessels. Vasa previa occurs in 1 in 2,500 births (4).
When vasa previa is diagnosed unexpectedly at delivery, more than half of affected babies are stillborn (4). However, when vasa previa is diagnosed by ultrasound earlier in pregnancy, fetal deaths generally can be prevented by delivering the baby by cesarean section at about 35 weeks of gestation (4).
Pregnant women with vasa previa sometimes have painless vaginal bleeding in the second or third trimester. A pregnant woman who experiences vaginal bleeding should always report it to her health care provider so that the cause can be determined and any necessary steps taken to protect the baby.
A pregnant woman may be at increased risk for vasa previa if she:
- Has a velamentous insertion of the cord (the umbilical cord inserts abnormally into the fetal membranes, instead of the center of the placenta)
- Has placenta previa (a low-lying placenta that covers part or all of the cervix) or certain other placental abnormalities
- Is expecting more than one baby
What is a nuchal cord?
About 25 percent of babies are born with a nuchal cord (the umbilical cord wrapped around the baby's neck) (1). A nuchal cord, also called nuchal loops, rarely causes any problems. Babies with a nuchal cord are generally healthy.
Sometimes fetal monitoring shows heart rate abnormalities during labor and delivery in babies with a nuchal cord. This may reflect pressure on the cord. However, the pressure is rarely serious enough to cause death or any lasting problems, although occasionally a cesarean delivery may be needed.
Less frequently, the umbilical cord becomes wrapped around other parts of the baby's body, such as a foot or hand. Generally, this doesn't harm the baby.
What are umbilical cord knots?
About 1 percent of babies are born with one or more knots in the umbilical cord (1). Some knots form during delivery when a baby with a nuchal cord is pulled through the loop. Others form during pregnancy when the baby moves around. Knots occur most often when the umbilical cord is too long and in identical-twin pregnancies. Identical twins share a single amniotic sac, and the babies' cords can become entangled.
As long as the knot remains loose, it generally does not harm the baby. However, sometimes the knot or knots can be pulled tight, cutting off the baby's oxygen supply. Cord knots result in miscarriage or stillbirth in 5 percent of cases (1). During labor and delivery, a tightening knot can cause the baby to have heart rate abnormalities that are detected by fetal monitoring. In some cases, a cesarean delivery may be necessary.
What is an umbilical cord cyst?
Umbilical cord cysts are outpockets in the cord. They are found in about 3 percent of pregnancies (2).
There are true and false cysts:
- True cysts are lined with cells and generally contain remnants of early embryonic structures.
- False cysts are fluid-filled sacs that can be related to a swelling of the Wharton's jelly.
Studies suggest that both types of cysts are sometimes associated with birth defects, including chromosomal abnormalities and kidney and abdominal defects (2). When a cord cyst is found during an ultrasound, the provider may recommend additional tests, such as amniocentesis and a detailed ultrasound, to diagnose or rule out birth defects.
Does the March of Dimes support research on umbilical cord abnormalities?
The March of Dimes continues to support research aimed at preventing umbilical cord abnormalities and the complications they cause. One grantee is studying the development of blood vessels in the umbilical cord for insight into the causes of single umbilical artery and other cord abnormalities. The goals of this study are to:
- Develop a better understanding of the causes of birth defects
- Develop treatments to help prevent oxygen deprivation before and during delivery, which may contribute to cerebral palsy and other forms of brain damage
- Cruikshank, D.W. Breech, Other Malpresentations, and Umbilical Cord Complications, in: Scott, J.R., et al. (eds.), Danforth's Obstetrics and Gynecology, 9th Edition. Philadelphia, Lippincott Williams and Wilkins, 2003, pages 381-395.
- Morgan, B.L.G. and Ross, M.G. Umbilical Cord Complications. emedicine.com, March 1, 2006.
- Gossett, D.R., et al. Antenatal Diagnosis of Single Umbilical Artery: Is Fetal Echocardiography Warranted? Obstetrics and Gynecology, volume 100, number 5, November 2002, pages 903-908.
- Oyelese, Y. and Smulian, J.C. Placenta Previa, Placenta Accreta, and Vasa Previa. Obstetrics and Gynecology, volume 107, number 4, April 2006, pages 927-941.