The umbilical cord acts as a lifeline that delivers essential oxygen and nutrients from the mother to the developing fetus. It also carries waste products away from the fetus back to the mother’s system. In some pregnancies, an atypical attachment of this cord occurs, known as velamentous cord insertion (VCI). This condition involves the umbilical cord attaching to the fetal membranes surrounding the placenta, rather than directly into the placental tissue itself. This article explores VCI, its influencing factors, associated risks, and how it is identified and managed.
Understanding Velamentous Cord Insertion
Typically, the umbilical cord inserts directly into the central portion of the placenta, allowing for efficient transfer of substances between mother and baby. This normal insertion ensures that the blood vessels within the cord are protected by a gelatinous substance called Wharton’s jelly. Wharton’s jelly cushions the delicate umbilical arteries and vein from compression, kinking, or rupture, maintaining a consistent blood flow to the fetus.
In contrast, velamentous cord insertion occurs when the umbilical cord attaches to the fetal membranes, which are the thin layers encasing the fetus and amniotic fluid, before the blood vessels reach the placenta. This means a segment of umbilical blood vessels travels unprotected through the membranes, outside Wharton’s jelly, before entering the placental tissue. This structural difference makes exposed vessels vulnerable to compression, damage, or rupture, potentially compromising blood and nutrients to the fetus.
Factors Influencing Velamentous Cord Insertion Development
The exact reasons for VCI development are unclear, but certain conditions and maternal factors are consistently associated with its occurrence, acting as risk factors rather than direct causes. Multiple gestations, particularly identical (monochorionic) twins who share a single placenta, have a significantly higher incidence of VCI, with rates potentially increasing tenfold compared to singleton pregnancies. In monochorionic twin pregnancies, VCI can also contribute to birth-weight discordance between the twins.
Assisted reproductive technologies (ART), such as in vitro fertilization (IVF), are also linked to a higher risk of VCI. This increased incidence in ART pregnancies may relate to the early stages of placental development and implantation. Additionally, certain placental anomalies, like placenta previa where the placenta covers the cervix, or an abnormally shaped or sized placenta, are associated with VCI.
Maternal factors can also play a role in the development of VCI. Advanced maternal age (over 35 years) has been identified as a risk factor. Smoking during pregnancy is also associated with an increased chance of VCI. Furthermore, some fetal conditions, including fetal growth restriction, have been observed more frequently in pregnancies with VCI.
Risks Associated with Velamentous Cord Insertion
The unprotected nature of the blood vessels in velamentous cord insertion can lead to several complications for both the mother and the baby. One of the most serious risks is vasa previa, a condition where these exposed fetal blood vessels cross over or lie very close to the internal opening of the cervix. If these vessels rupture during labor, especially when the membranes break, it can result in rapid and severe blood loss for the fetus, which can be life-threatening.
VCI can also impair the efficiency of nutrient and oxygen transfer to the fetus, potentially leading to fetal growth restriction (FGR) or the birth of babies who are small for their gestational age. There is an increased risk of preterm birth (before 37 weeks of gestation).
During labor, unprotected vessels are susceptible to compression, causing fetal distress (abnormal fetal heart rate patterns). This can necessitate an emergency C-section. While less common, VCI may also be associated with placental abruption, where the placenta separates from the uterine wall prematurely.
Identifying and Monitoring Velamentous Cord Insertion
VCI is primarily diagnosed through ultrasound imaging during pregnancy. It is often identified during the routine second-trimester anatomy scan, typically performed around 18 to 22 weeks of gestation, where a detailed assessment of the placenta and cord insertion site is conducted. Color Doppler ultrasound helps visualize blood flow and confirm cord attachment.
Once diagnosed, VCI pregnancies are carefully monitored for complications. This often involves regular ultrasound surveillance to assess fetal growth and overall well-being, sometimes as frequently as every four weeks starting around 28 weeks. Non-stress tests, which monitor the baby’s heart rate in response to movement, may also be performed to ensure adequate blood flow.
Delivery planning is a crucial aspect of managing VCI. If vasa previa is also present, a planned C-section is often recommended, usually around 34 to 36 weeks of gestation, to avoid the risks associated with vaginal delivery and potential vessel rupture. In cases of isolated VCI without vasa previa, a vaginal delivery may still be possible with close monitoring of the baby’s heart rate during labor. With proper diagnosis and careful management, outcomes for VCI pregnancies are often positive.