Definition/General
Introduction:
Single umbilical artery (SUA) is the most common vascular anomaly of the umbilical cord
It occurs in 0.5-1% of singleton pregnancies and 5-7% of twin pregnancies
The condition is characterized by absence of one umbilical artery, resulting in a two-vessel cord instead of the normal three-vessel cord.
Origin:
Results from either primary agenesis of one umbilical artery or secondary atrophy/thrombosis during development
The missing artery may be left or right
Remaining artery undergoes compensatory hypertrophy
Associated with abnormal cord coiling.
Classification:
Classified as isolated SUA or associated with other anomalies
True agenesis versus secondary atrophy
Left artery absent (more common) versus right artery absent
May be associated with chromosomal abnormalities.
Epidemiology:
Incidence: 0.5-1% singleton pregnancies
5-7% twin pregnancies
Higher incidence in diabetic mothers
More common with advanced maternal age
Associated with 20-30% of fetal anomalies.
Clinical Features
Presentation:
Intrauterine growth restriction (IUGR) in 15-20% cases
Preterm delivery more common
Associated congenital anomalies
Oligohydramnios
Abnormal fetal heart rate patterns.
Symptoms:
Fetal growth restriction
Decreased fetal movements
Abnormal cardiotocography
Meconium-stained liquor
Preterm labor
Emergency cesarean section indication.
Risk Factors:
Maternal diabetes mellitus
Advanced maternal age
Previous pregnancy losses
Family history of congenital anomalies
Genetic syndromes
Multiple pregnancy.
Screening:
Ultrasound examination at 18-20 weeks
Color Doppler assessment of cord vessels
Cross-sectional cord imaging
Detailed anomaly scan
Genetic counseling recommended.
Master Single Umbilical Artery Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Umbilical cord contains two vessels instead of normal three
One artery and one vein present
Cord may appear thinner than normal
Wharton's jelly distribution may be altered.
Characteristics:
Remaining artery may show compensatory enlargement
Cord coiling often abnormal (hypocoiled)
May show areas of thrombosis or fibrosis
Vessel caliber assessment important.
Size Location:
Cord diameter may be reduced
Normal cord length usually maintained
Cross-sectional examination reveals two vessels
Vessel distribution within Wharton's jelly altered.
Multifocality:
Usually affects entire cord length
May have focal vessel remnants
Associated with other cord anomalies
Placental surface vessels may be altered.
Microscopic Description
Histological Features:
Cross-section shows one artery and one vein
Absent arterial structure may leave remnant tissue
Normal vessel wall architecture in remaining vessels
Wharton's jelly shows normal composition.
Cellular Characteristics:
Remaining artery shows normal smooth muscle
Intact endothelial lining
Umbilical vein structure normal
Compensatory hypertrophy may be evident
No inflammatory changes.
Architectural Patterns:
Two-vessel pattern throughout cord length
Normal spiral arrangement may be altered
Wharton's jelly distribution modified
Vessel wall thickness may be increased.
Grading Criteria:
Assessment of vessel count in multiple sections
Compensatory changes evaluation
Associated anomalies documentation
Thrombosis or fibrosis assessment.
Immunohistochemistry
Positive Markers:
CD31 highlights endothelial cells
CD34 marks vessel endothelium
Smooth muscle actin in arterial walls
Desmin in smooth muscle
Factor VIII related antigen positive.
Negative Markers:
Cytokeratin negative in vessels
Vimentin negative in endothelium
No specific negative markers required
Normal vascular immunophenotype.
Diagnostic Utility:
Confirms vessel count in questionable cases
Identifies vessel remnants
Useful in cord cross-sections
Excludes other vascular anomalies
Quality control for vessel counting.
Molecular Subtypes:
No specific molecular classification
Normal vascular markers present
Standard endothelial and smooth muscle patterns
Morphological diagnosis remains gold standard.
Molecular/Genetic
Genetic Mutations:
Associated with chromosomal abnormalities in 15-20% cases
Trisomy 18 most common
Trisomy 13 association
Turner syndrome
Single gene mutations rare.
Molecular Markers:
Normal vascular development markers
VEGF pathways may be altered
Angiogenesis factors involved
Developmental gene expression may be modified.
Prognostic Significance:
Isolated SUA: generally good prognosis
Associated anomalies: variable prognosis
Increased perinatal morbidity
IUGR risk 15-20%
Preterm delivery risk increased.
Therapeutic Targets:
No specific therapeutic targets
Enhanced fetal monitoring recommended
Growth assessment important
Genetic counseling
Delivery planning optimization.
Differential Diagnosis
Similar Entities:
Normal three-vessel cord
Cord thrombosis with secondary vessel loss
Cord compression artifacts
Processing artifacts
Cord hematoma.
Distinguishing Features:
SUA: two vessels throughout cord length
SUA: no evidence of thrombosis
Normal: three vessels present
Thrombosis: evidence of clot
Artifact: processing-related changes.
Diagnostic Challenges:
Artifact distinction from true anomaly
Vessel counting in multiple sections
Recognition of vessel remnants
Documentation requirements
Clinical correlation important.
Rare Variants:
Supernumerary vessels (four-vessel cord)
Cord aplasia (absent cord)
Persistent right umbilical vein
Combined vascular anomalies
Arterial-venous malformations.
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
Umbilical cord measuring [X] cm in length with [normal/abnormal] coiling
Vessel Configuration
Cross-sectional examination reveals [number] arteries and [number] veins (two-vessel cord)
Vessel Morphology
Remaining vessels show [normal/compensatory] morphology with [present/absent] hypertrophy
Wharton's Jelly
Wharton's jelly: [normal/altered] distribution around vessels
Associated Findings
Associated findings: [present/absent] other cord anomalies
Microscopic Findings
Microscopic examination confirms two-vessel cord with [normal/abnormal] vessel morphology
Clinical Significance
Clinical significance: [risk assessment] for fetal anomalies, genetic counseling recommended
Final Diagnosis
Single umbilical artery (two-vessel cord)