Velamentous cord insertion occurs when the placental end of the umbilical cord contains divergent vessels that are surrounded by membranes and are not supported by Whartons Jelly.

Abstract: Velamentous cord insertion is defined as placental insertion of the umbilical cord into the membranes. Membranous vessels can also be seen when they arise from a marginal cord insertion with aberrant vessels or they may also connect two lobes of the placenta (bilobed placenta or succenturiate lobe). Since these vessels are not covered in Whartons jelly (protective covering of the umbilical cord), they are prone to compression and or rupture. Complications are also more frequent if these membranous vessels pass in front of the cervical os- also known as vasa previa. If these complications arise, they may increase perinatal morbidity and mortality. 

Keywords: Velamentous, cord, insertion

Authors: Dina Zaki 1

1. CHU Ste Justine, Department of Obstetrics and Gynecology, Division of Maternal Fetal Medicine 

Reviewers: Karen Fung-Kee-Fung, Felipe Moretti 

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Velamentous cord insertion occurs when the placental end of the umbilical cord contains divergent vessels that are surrounded by membranes and are not supported by Whartons Jelly. There is no minimal length of exposed vessels needed to define a velamentous cord insertion. Therefore there can be high variability between where the cord vessels insert into the membranes and their placental insertion site. 

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Velamentous cord insertion is seen in about 1 percent of singleton gestations (1) but can be seen more frequently in monochorionic twin gestations (2-4). It is also more commonly associated with placenta praevia. Prevalence is also higher in stillbirths, particularly during multi-fetal pregnancies. (4)


The pathogenesis is currently unknown. One hypothesis is that the cord’s initial insertion site occurs centrally but becomes peripheral as the cord is unable to follow the physiological “migration” of a low lying placenta This results in one half migrating towards the more highly vascularized myometrium while the other half involutes, thereby creating a membranous  cord insertion. The association between placenta previa and marginal cord insertion supports this current hypothesis. (5)

Associated anomalies

Velamentous cords contain a single umbilical artery in about 12% of cases (5)

Recurrence risk

The recurrence risk is the same as baseline risk for velamentous cord insertion (1% in singleton pregnancies and more frequently in monochorionic twin gestations).


Diagnosis is made with ultrasound and confirmed with gross examination. With velamentous cord insertion, the normal cord with its protected vessels within can end several centimetres from the placental cake , the unprotected vessels then may continue to course through the membranes,  diverge  from each other and cross between the chorion and the amnion before inserting  into the placenta. When seen in monochorionic twins, the unprotected vessels are often seen within the dividing membrane. 
On ultrasound, the vessels from the umbilical cord lie parallel to the uterine wall as they enter the placenta and connect to the vasculature of the chorion. If the fetus or uterus is moved by the sonographer and the vessels do not remain stationary, this is diagnostic of a loop of cord. If the vessels remain immobile, this is diagnostic of the cord insertion location. (6) Gray scale ultrasound should show images in sagittal and transverse views of the cord inserting into the membranes as opposed to the placenta. Color Doppler can confirm the diagnosis by showing that the blood flow in these vessels is of fetal origin. If cord insertion is close to the cervix/lower uterus, or diagnosis is uncertain, transvaginal ultrasound should be done to confirm the diagnosis and rule out vasa previa, again using color Doppler to confirm vessels are of fetal origin. 
Second trimester ultrasound has shown high specificity (>99,8%) and positive predictive value (83%-100%). However, variation is seen in sensitivity between different studies, ranging from 25%-100%. When transabdominal ultrasound is insufficient, using transvaginal ultrasound can increase sensitivity up to 100%. (7)

Differential diagnosis

Differential diagnosis includes a free loop of cord.  If the vessels move as the sonographer manipulates the uterus or fetus, the diagnosis is a free loop of cord. 

Implications for sonographic diagnosis

Sonographic diagnosis is confirmed when imaging the umbilical cord insertion during the second trimester ultrasound. Color Doppler can enhance images and increases diagnostic sensitivity to 69-100% and specificity to 95-100%. Imaging the cord insertion at multiple sites and planes may also improve ultrasonographic diagnosis. (1, 8)

Implications for sonographic screening

Most obstetrical guidelines will recommend that in the second and third trimesters, the umbilical cord should be imaged and the number of vessels in the cord should also be documented. The placental cord insertion site should be also documented whenever technically possible during these ultrasounds. Even when this has been accomplished, the diagnosis of velamentous cord insertion may be missed. Failure to make this diagnosis is therefore not a breach of standard of care. (9) Detection of an umbilical cord insertion in the lower third of the uterus during the first trimester is predictive of an abnormal cord insertion at delivery, particularly a velamentous one. (10,11)

Additional transvaginal color Doppler ultrasonography is recommended in cases of velamentous cord insertion suspected at the lower edge of the placenta to rule out vasa previa. (6)

When Vasa Previa is diagnosed, VCI has been reported to be present in approximately 76%; however, the inverse is not seen and only the minority of VCI is associated with Vasa Previa. ( )


The clinical course in documented velamentous cord insertion is usually benign, but in some cases may be complicated by kinking of the cord or compression of the vessels. These complications can increase the chances or mortality and morbidity, including both preterm birth and growth restriction. (12-13) Rupture of the fetal membranes may cause rupture of the vessels, although this will typically only occur when the vessels are close to or cover the cervix (vasa previa) (14). 
Membranous vessels of longer lengths , commencing their insertion  into the membranes farther from placental site,  are more prone to kinking. Membranous vessels closer to (but not lying over) the cervix are also at risk for compression during fetal descent in labor (13). 
A meta-analysis evaluating the risk between risk of preterm birth and placental implantation abnormalities found that in velamentous cord insertion, there was a higher preterm birth rate (RR 1,95) increased neonatal intensive care admissions (RR 1,76), SGA babies (RR 1,69) and perinatal death (RR 2,15). (12). However, in this analysis, the majority of the included studies did not have a control group and were quite small. Other larger studies have continued to show some adverse perinatal outcomes associated with velamentous cord insertion such as growth restriction (16,9% vs 10,1%), and IUFD (2,6% vs 0.28%). (13, 15, 16)
When seen in monochorionic twins, velamentous cord insertion is associated with discordant growth and selective fetal growth restriction as well as twin-twin transfusion syndrome. (17)

In multiple gestations, studies done on velamentous cord insertion showed that adverse outcomes were not increased with dichorionic twins but that in monochorionic twin gestations the risks of adverse outcomes were slightly higher. (18) These outcomes include severe birth weight discordance (OR 4,76), SGA (OR 1,66) and IUFD (OR 2,71). (18)

Maternal Prognosis

When the cord inserts vellamentously, maternal risks are increased with slightly higher  chance  of requiring  manual removal of the placenta (14,4% vs 0.7%) in both vaginal and cesarian birth as well as post-partum hemorrhage (6,6% vs 2,8%) (16). 


Currently there is no large data from large or controlled studies for management of velamentous cord insertion. Management is therefore based on small studies/reports, expert opinion and clinical judgement.
If ultrasound during the second trimester suggest velamentous cord insertion the following has been recommended: 
1-    detailed fetal anatomic survey, including evaluation for vasa previa
2-    Serial growth assessment every 4-6 weeks beginning at 24 weeks gestation
3-    Serial assessment of cord insertion at time of fetal growth ultrasounds
4-    Delivery by 40 weeks gestation: (to decrease the risk of decreasing fetal amniotic fluid which would increase risk of vessel compression). 
5-    Continuous fetal heart rate monitoring during labor. 
6-    No cord traction (or very limited traction) after delivery to avoid avulsion. 


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This article should be cited as: Zaki, Dina: Velamentous cord insertion, Visual Encyclopedia of Ultrasound in Obstetrics and Gynecology,, September 2022

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