Understanding Velamentous Cord Insertion
Velamentous Cord Insertion (VCI) is an anatomical variation in pregnancy where the umbilical cord connects to the fetal membranes, the amnion and chorion, before reaching the placenta. Typically, the umbilical cord inserts directly into the central or eccentric mass of the placenta, where the blood vessels are protected by a gelatinous substance called Wharton’s jelly. In VCI, the vessels must travel unprotected across the membranes to reach the placental tissue. This happens in about 1% of singleton pregnancies, but the prevalence is much higher in multiple gestations, such as twins, where it can occur up to 22% of the time, especially in those sharing a single placenta.
This absence of Wharton’s jelly protection leaves the vessels vulnerable to compression, kinking, or rupture, which can impair the transfer of nutrients and oxygen to the fetus. Diagnosing VCI is accomplished through ultrasound, often during the second-trimester anatomy scan. Color Doppler imaging is particularly helpful for visualizing the blood flow and confirming the cord’s exact insertion point into the membranes.
Addressing the Possibility of Correction
The fundamental question of whether Velamentous Cord Insertion can correct itself must be answered: the anatomical insertion point of the umbilical cord does not physically change once established in the membranes. The cord’s initial point of attachment is a fixed structure that cannot migrate back into the placenta’s central mass. Therefore, the diagnosis of VCI itself is permanent.
The confusion about “correction” often arises from a phenomenon known as placental migration or trophotropism. The placenta is a dynamic organ that grows throughout pregnancy, often expanding toward areas of the uterus with better blood supply. This growth can cause the entire placental mass to shift its relative position within the uterus over time. This placental remodeling can sometimes make the velamentous insertion site appear less marginal or less threatening on later ultrasound scans. However, the unprotected nature of the vessels traversing the membranes remains a feature of the pregnancy.
Clinical Implications and Associated Risks
The presence of Velamentous Cord Insertion elevates the risk for several complications due to the exposed vessels. The most significant association is with Vasa Previa, where the unprotected vessels pass directly over the internal cervical opening. If the membranes rupture during labor, these exposed vessels are at extremely high risk of tearing, leading to rapid and catastrophic fetal blood loss.
Even without Vasa Previa, the unprotected vessels are susceptible to external pressure or kinking, which can disrupt the flow of blood and nutrients. This chronic compression contributes to a significantly higher risk of Fetal Growth Restriction (FGR), where the fetus does not grow at the expected rate. Studies indicate that VCI is associated with up to a 4.3-fold increased risk of FGR.
VCI is also linked to a higher incidence of preterm birth, with the risk increasing by up to 4.6 times. The condition can also increase the likelihood of placental abruption, where the placenta prematurely separates from the uterine wall. These factors combined mean that VCI is not a benign finding and requires specialized care.
Monitoring and Delivery Management
A diagnosis of Velamentous Cord Insertion necessitates increased surveillance. Monitoring typically involves serial ultrasounds to track fetal growth and amniotic fluid levels. Doppler studies are also regularly used to assess blood flow through the umbilical cord and fetal vessels.
Special attention is given to ruling out Vasa Previa, which is accomplished using color Doppler and transvaginal ultrasound to check for vessels near the cervix. In the third trimester, additional fetal surveillance, such as Nonstress Tests or Biophysical Profiles, may be employed to look for signs of distress or reduced oxygen supply. These tests monitor the baby’s heart rate and movement patterns.
The delivery plan is influenced by whether Vasa Previa is confirmed or suspected alongside the VCI. If Vasa Previa is present, a scheduled Cesarean section is recommended, often around 34 to 36 weeks of gestation, to prevent vessel rupture during labor. For isolated VCI cases without other complications, a trial of vaginal delivery may still be considered, but it requires continuous fetal heart rate monitoring throughout labor to detect any signs of cord compression or distress.