What Is Velamentous Cord Insertion?

Medically Reviewed by Traci C. Johnson, MD on April 19, 2023
4 min read

The umbilical cord is your baby's lifeline. It carries nutrient-rich blood and oxygen to the baby and removes waste. Problems with the umbilical cord can cause issues during pregnancy or during delivery. Velamentous cord insertion is one such condition.

Velamentous cord insertion affects the baby's connection to the placenta, which develops when you are pregnant.  The placenta is a unique organ that contains tissue from both the baby and the mother. The exchanges of oxygen, nutrients, and waste take place in the placenta.

The placenta attaches to the wall of the uterus, and the umbilical cord connects it to the baby. Normally, the umbilical cord is attached to the center of the placenta, but unusual placements can occur. The cord can attach off-center, which is usually not a problem. In marginal cord insertion, the cord attaches to the edge of the placenta, which can cause some problems. 

Velamentous cord insertion is a rarer issue. In this condition, the cord doesn't attach directly to the placenta but instead attaches to other membranes in the uterus. 

When this abnormality occurs, the blood vessels are naked as they pass through the membranes. They aren't protected by the umbilical cord for their full length. They also lack the protection of the gel-like substance that fills the umbilical cord and cushions the blood vessels. This lack of protection makes the blood vessels more likely to become compressed or to break.

No one knows what causes velamentous cord insertion, but researchers have identified several risk factors. It happens more often in pregnancies involving twins. It occurs in about 1% of pregnancies resulting in one child but in almost 9% of twin pregnancies. The rate is higher when the twins share a single or fused placenta. The rate is lower for twins who have separate placentas. 

Velamentous cord insertion is also more likely when pregnancy happens through the use of fertility treatments such as in-vitro fertilization. It may be more likely in older mothers and in first pregnancies. The mother's health may also affect the risk of unusual cord insertions. Mothers who smoke or who have chronic diseases such as diabetes may be at higher risk.

Miscarriages that happen from the ninth to the 16th week are often associated with problems with the umbilical cord, including velamentous cord insertion. 

Although most women have ultrasounds during their pregnancies, the place where the cord attaches to the placenta can be hard to see on ultrasounds, making it difficult to diagnose velamentous cord insertion. When velamentous cord insertion is diagnosed during pregnancy, it is usually during an ultrasound performed in the second trimester. As the baby enters the third trimester, unusual cord insertions can be harder to detect.

If you or your baby have unusual symptoms during pregnancy, it can also lead to a diagnosis. The mother may have vaginal bleeding, or the baby may have a slow heart rate. If such symptoms occur, the doctor may order extra ultrasounds, leading to the diagnosis of an unusual cord insertion. 

Special technology can increase the detection rate of a velamentous cord insertion. A color Doppler ultrasound can detect velamentous cord insertion with 99% accuracy in a research setting. Standard ultrasounds are less likely to find unusual cord placements.

Velamentous cord insertion can cause vasa previa, which means the unprotected blood vessels lie between the baby and the mother's birth canal. When labor begins, the blood vessels may break, putting the baby at risk of serious blood loss. If the blood vessels don't break, the baby can still suffer a lack of oxygen due to pressure on the blood vessels.

If the unusual cord insertion is diagnosed before delivery, doctors usually monitor the baby's health using non stress testing. These tests check the baby's heart rate as the baby moves. The results give information about the baby's oxygen supply. Such tests are called non stress because no extra strain is put on the baby. 

When doctors diagnose vasa previa, they may take the following steps:

  • Monitor the baby beginning at around 28 weeks, often performing twice-weekly non stress tests
  • Offer hospital admission at around 30 or 32 weeks for continuous monitoring or for more frequent tests
  • Use corticosteroids to help the baby's lungs develop
  • Schedule a Cesarean section sometime after 34 weeks
  • Perform an emergency Cesarean section if the membranes break or if significant vaginal bleeding occurs 

Other outcomes are possible with velamentous cord insertion. Low birth weight is one of the most common. Some studies suggest that babies with velamentous cord insertion are more likely to be delivered early and to require care in a neonatal intensive care unit. Also, babies may have lower scores on the Apgar, a test used to measure a baby's health at birth.

Velamentous cord insertion can cause problems for mothers, too. They are more likely to have a hemorrhage (uncontrolled bleeding). The placenta may need to be removed manually instead of being delivered in the usual way. Some curettage or scraping of the uterus may be necessary.