Definition/General
Introduction:
Velamentous cord insertion is a developmental anomaly where the umbilical cord vessels traverse the fetal membranes before reaching the placental parenchyma
It occurs in 1-2% of singleton pregnancies and 15-20% in multiple gestations
The condition is characterized by absence of Wharton's jelly protection around vessels in membranes.
Origin:
Results from abnormal implantation or migration of the blastocyst
The cord vessels reach the placenta by crossing the chorioamniotic membranes
Vessels are supported only by a thin layer of amnion and chorion
This creates vulnerability to compression and rupture.
Classification:
Classified by distance from placental margin
True velamentous insertion: vessels traverse membranes
Marginal cord insertion: within 2 cm of placental edge
Vasa previa: when vessels cross internal cervical os
Associated with bipartite or succenturiate placenta.
Epidemiology:
Incidence: 1-2% singleton pregnancies
15-20% in twin pregnancies
Higher risk with assisted reproductive technology
More common in advanced maternal age
Associated with placental abnormalities
Risk factors include previous uterine surgery.
Clinical Features
Presentation:
Asymptomatic in most cases
Antepartum bleeding if associated with vasa previa
Abnormal fetal heart rate patterns
Intrauterine growth restriction (IUGR)
Oligohydramnios
Preterm labor.
Symptoms:
Maternal bleeding (vasa previa cases)
Fetal distress during labor
Cord compression symptoms
Sudden fetal bradycardia
Abnormal cardiotocography patterns
Emergency cesarean section indication.
Risk Factors:
Multiple gestation pregnancies
In vitro fertilization pregnancies
Advanced maternal age (>35 years)
Previous uterine surgery
Placental abnormalities
Bipartite placenta
Succenturiate lobes.
Screening:
Ultrasound examination for cord insertion site
Color Doppler to identify vasa previa
Routine examination at 18-20 weeks
Transvaginal ultrasound for better visualization
Serial monitoring in high-risk cases.
Master Velamentous Cord Insertion Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Umbilical cord inserts into the fetal membranes rather than placental parenchyma
Vessels run between amnion and chorion before entering placenta
Absence of Wharton's jelly protection in membrane portion
Vessels appear as raised ridges on membrane surface.
Characteristics:
Cord vessels branch before reaching placental margin
Vessels are unsupported and vulnerable
May show evidence of thrombosis or rupture
Associated with membrane discoloration
Placenta may show areas of infarction.
Size Location:
Variable distance from placental margin (>2 cm)
Vessels may traverse entire membrane length
Common sites include lower uterine segment
May cross the internal cervical os (vasa previa)
Associated with low-lying placenta.
Multifocality:
May involve single or multiple vessels
Arteries and veins affected
May be associated with single umbilical artery
Bipartite placenta commonly associated
Succenturiate lobes frequently present.
Microscopic Description
Histological Features:
Umbilical vessels traversing fetal membranes without Wharton's jelly
Vessels supported only by thin amnion and chorion
May show fibrin deposition around vessels
Evidence of hemorrhage in adjacent membranes.
Cellular Characteristics:
Normal umbilical artery and vein structure
Smooth muscle in arterial walls
Endothelial lining intact or damaged
Absence of mucoid connective tissue (Wharton's jelly)
Chorioamniotic membranes show normal structure.
Architectural Patterns:
Vessels run in parallel arrangement within membranes
May show branching pattern before placental entry
Thrombosis may be present in affected vessels
Surrounding membranes may show inflammatory changes.
Grading Criteria:
Classification based on vessel involvement
Complete velamentous: all vessels in membranes
Partial velamentous: some vessels protected
Distance measurement from placental margin
Assessment for vasa previa configuration.
Immunohistochemistry
Positive Markers:
CD31 highlights endothelial cells
CD34 marks vascular endothelium
Smooth muscle actin in arterial walls
Desmin in smooth muscle
Factor VIII related antigen in endothelium.
Negative Markers:
Cytokeratin negative in vessels
Vimentin negative in endothelium
No specific negative markers
Trophoblast markers negative in vessels
Normal vessel morphology on routine stains.
Diagnostic Utility:
Helps identify vascular structures in membranes
Useful in fragmented specimens
Confirms endothelial integrity
Identifies thrombosed vessels
Distinguishes from other membrane lesions.
Molecular Subtypes:
No specific molecular subtypes
Normal vascular markers expressed
No diagnostic molecular features
Standard endothelial and smooth muscle markers
Morphological diagnosis remains gold standard.
Molecular/Genetic
Genetic Mutations:
No specific genetic mutations identified
May be associated with developmental anomalies
Possible genetic predisposition in families
Chromosomal abnormalities may be associated
Polygenic inheritance suspected.
Molecular Markers:
Normal vascular development markers
VEGF expression in vessel formation
Normal endothelial markers
Placental development genes may be involved
No specific diagnostic markers.
Prognostic Significance:
Associated with increased perinatal morbidity
Higher risk of preterm delivery
IUGR more common
Increased cesarean section rate
Vasa previa associated with high fetal mortality.
Therapeutic Targets:
No specific therapeutic targets
Early detection crucial for management
Cesarean delivery recommended for vasa previa
Antenatal steroid administration
Delivery timing optimization.
Differential Diagnosis
Similar Entities:
Marginal cord insertion (cord within 2 cm of edge)
Normal cord insertion (central or paracentral)
Chorioamniotic hemorrhage
Placental abruption
Amnion nodosum.
Distinguishing Features:
Velamentous: vessels in fetal membranes
Velamentous: absence of Wharton's jelly
Marginal: cord within 2 cm of margin
Marginal: some Wharton's jelly present
Normal: central or paracentral insertion
Abruption: retroplacental clot.
Diagnostic Challenges:
Distinguishing from marginal insertion
Identifying in fragmented membranes
Recognition of vasa previa
Correlation with clinical history
Measurement of distance from placental edge.
Rare Variants:
Battledore placenta (marginal insertion variant)
Circumvallate placenta with velamentous insertion
Bipartite placenta with connecting vessels
Velamentous insertion with single umbilical artery.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Placenta with umbilical cord measuring [X] cm in length
Cord Insertion Site
Cord insertion: [velamentous/marginal/central], [X] cm from placental margin
Vessel Configuration
Vessels: [number] arteries, [number] veins, [normal/abnormal] course through membranes
Membrane Examination
Membranes show [normal/abnormal] vessels with [presence/absence] of Wharton's jelly protection
Placental Findings
Placenta: [weight] grams, [normal/abnormal] parenchyma, [present/absent] infarcts
Microscopic Findings
Microscopic examination shows [vessel description] with [normal/abnormal] endothelium
Clinical Significance
Clinical significance: [risk assessment] for fetal complications
Final Diagnosis
Velamentous cord insertion, [distance] from placental margin