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Umbilical Vein
The umbilical vein is the fetal vessel that carries relatively oxygenated, nutrient-rich blood from the placenta to the fetus. The single left umbilical vein travels through the umbilical cord, enters the fetal abdomen at the umbilicus, and reaches the liver, where blood enters the hepatic circulation or passes through the ductus venosus toward the inferior vena cava.
RegionAbdomen
SystemCardiovascular System
The umbilical vein is the fetal blood vessel that carries relatively oxygenated and nutrient-rich blood from the placenta toward the fetus. It is one of the major vessels of the umbilical cord and forms the principal route by which oxygen and nutrients obtained through placental exchange enter the fetal circulation.
The normal umbilical cord contains one umbilical vein and two umbilical arteries. The vein carries blood from the placenta to the fetus, while the paired arteries carry relatively deoxygenated fetal blood in the opposite direction toward the placenta.
After entering the fetal abdomen at the umbilicus, the umbilical vein travels toward the liver. Some of its blood enters the hepatic circulation, while a substantial portion is directed through the ductus venosus toward the inferior vena cava. After birth, the umbilical vein closes and its intra-abdominal remnant becomes the ligamentum teres hepatis, or round ligament of the liver.
Number
Although paired umbilical veins are present early in embryonic development, the mature fetal circulation normally contains a single functional umbilical vein.
This vessel is derived predominantly from the persistent left umbilical vein.
Direction of Blood Flow
The umbilical vein carries blood from the placenta toward the fetal heart.
Its direction can be summarized as:
Placenta → Umbilical vein → Fetal liver → Ductus venosus / hepatic circulation → Inferior vena cava → Right atrium
Why It Is Called a Vein
Veins are defined by carrying blood toward the heart rather than by the oxygen content of their blood.
The umbilical vein therefore remains a vein even though it carries the most highly oxygenated blood within the fetal circulation.
Oxygen Content
Blood in the umbilical vein has a higher oxygen content than blood in the fetal systemic arteries because it has recently passed through the placenta.
Its oxygen content gradually decreases as it mixes with blood from other fetal vascular territories.
Placental Origin
The umbilical vein forms from venous channels collecting blood from the fetal capillary networks of the placenta.
These vessels converge across the fetal surface of the placenta and ultimately form the single umbilical vein entering the umbilical cord.
Placental Exchange
The placenta allows exchange between maternal and fetal circulations without normal direct mixing of their blood.
Oxygen and nutrients move toward the fetal circulation, while carbon dioxide and metabolic waste products move toward the maternal circulation.
Chorionic Villi
Fetal capillaries within the chorionic villi lie close to maternal blood within the intervillous spaces.
After exchange, fetal blood drains from the villous capillary networks into progressively larger veins that contribute to the umbilical vein.
Course Through the Umbilical Cord
The umbilical vein travels through the umbilical cord with the two umbilical arteries.
All three vessels are surrounded by Wharton's jelly, a specialized connective tissue that helps protect them against compression and mechanical distortion.
Umbilical Cord Vessel Arrangement
| Vessel | Number | Direction | Relative Oxygen Content |
|---|---|---|---|
| Umbilical vein | One | Placenta → Fetus | Higher |
| Umbilical arteries | Two | Fetus → Placenta | Lower |
Wharton's Jelly
Wharton's jelly is rich in extracellular matrix and water and surrounds the umbilical vessels.
It provides structural support and helps preserve blood flow when the cord bends, twists, or is exposed to external pressure.
Entry Into the Fetal Abdomen
The umbilical vein enters the fetal body through the umbilical ring at the umbilicus.
From there, it courses superiorly toward the inferior surface of the liver.
Course Toward the Liver
Within the fetal abdomen, the umbilical vein travels in the free margin of the falciform ligament toward the liver.
It reaches the hepatic region where its blood is distributed between the hepatic circulation and the ductus venosus.
Relationship to the Falciform Ligament
The intra-abdominal umbilical vein is closely associated with the developing falciform ligament.
After birth, its fibrous remnant, the ligamentum teres hepatis, remains within the free inferior margin of the falciform ligament.
Relationship to the Liver
The fetal liver receives a portion of the oxygenated blood arriving through the umbilical vein.
This placental blood contributes to hepatic perfusion and supports the rapidly developing fetal liver.
Hepatic Sinusoids
Some umbilical venous blood enters the hepatic sinusoids, where it mixes with blood from the portal venous circulation.
Blood leaving the hepatic circulation then reaches the inferior vena cava through the hepatic veins.
Relationship to the Ductus Venosus
The ductus venosus is a fetal vascular channel that allows a substantial portion of umbilical venous blood to bypass much of the hepatic sinusoidal circulation.
It directs blood rapidly toward the inferior vena cava.
Two Major Pathways Through the Liver
| Pathway | Route | Function |
|---|---|---|
| Hepatic pathway | Umbilical vein → Hepatic sinusoids → Hepatic veins → IVC | Perfuses fetal liver |
| Ductus venosus pathway | Umbilical vein → Ductus venosus → IVC | Bypasses much of hepatic microcirculation |
Inferior Vena Cava
Blood passing through the ductus venosus enters the central venous circulation and reaches the inferior vena cava.
Here it mixes with less oxygenated venous blood returning from the lower fetal body and hepatic circulation.
Entry Into the Right Atrium
The inferior vena cava carries this mixed blood into the right atrium.
Because of fetal intracardiac anatomy and flow patterns, much of the relatively oxygen-rich stream is directed toward the foramen ovale.
Relationship to the Foramen Ovale
The foramen ovale allows blood to pass from the right atrium into the left atrium during fetal life.
This pathway enables a substantial portion of the oxygen-rich blood originally delivered through the umbilical vein to bypass the right ventricle and fetal pulmonary circulation.
Left-Sided Cardiac Pathway
Blood crossing the foramen ovale enters the left atrium and then the left ventricle.
The left ventricle ejects it into the ascending aorta, where relatively well-oxygenated blood is preferentially distributed to the coronary circulation, head, neck, and upper limbs.
Preferential Streaming
Blood entering the fetal right atrium does not undergo complete homogeneous mixing.
Flow from the inferior vena cava is preferentially directed toward the foramen ovale, helping preserve relatively high oxygen content in blood entering the left side of the heart.
Supply to the Developing Brain
The preferential delivery of relatively oxygen-rich blood into the ascending aorta supports oxygen delivery to the developing brain.
This distribution is an important feature of the organization of fetal circulation.
Supply to the Coronary Circulation
The coronary arteries arise from the ascending aorta and receive blood ejected by the left ventricle.
The fetal streaming pattern therefore also helps supply relatively oxygen-rich blood to the myocardium.
Role in Fetal Circulation
The umbilical vein is the principal vascular connection carrying oxygen and nutrients from the placenta into the fetus.
Its functions include:
- Transport of oxygenated placental blood
- Delivery of nutrients absorbed through the placenta
- Perfusion of the fetal liver
- Supply of blood to the ductus venosus
- Contribution to preferential oxygen delivery to the heart and brain
Relationship to the Umbilical Arteries
The umbilical arteries and vein together form the vascular circuit connecting the fetus and placenta.
The arteries carry blood toward the placenta, and the vein returns blood after placental exchange.
Fetoplacental Circulatory Loop
A simplified loop can be represented as:
Fetus → Umbilical arteries → Placenta → Umbilical vein → Fetus
Relationship to the Ductus Arteriosus
Much of the less oxygenated blood entering the fetal right ventricle is ejected into the pulmonary trunk and then passes through the ductus arteriosus into the descending aorta.
This blood eventually contributes to flow through the umbilical arteries back toward the placenta.
The Three Major Fetal Shunts
| Shunt | Connection | Primary Role |
|---|---|---|
| Ductus venosus | Umbilical venous pathway to IVC | Partial bypass of hepatic sinusoids |
| Foramen ovale | Right atrium to left atrium | Bypass of pulmonary circulation at atrial level |
| Ductus arteriosus | Pulmonary arterial system to descending aorta | Bypass of most pulmonary blood flow |
Embryological Development
Early in embryonic development, paired umbilical veins carry blood from the chorion toward the embryonic heart.
As venous development progresses, extensive remodeling occurs in association with development of the liver.
Right Umbilical Vein
The right umbilical vein normally degenerates during development.
Its regression leaves the left umbilical vein as the principal placental venous channel.
Left Umbilical Vein
The left umbilical vein persists and becomes the definitive umbilical vein of later fetal life.
It establishes connections with the developing hepatic circulation and ductus venosus.
Development of the Hepatic Connections
As hepatic cords grow into the septum transversum, they interrupt and remodel the embryonic venous channels.
This process creates hepatic sinusoids and establishes the pathways through which umbilical blood reaches the liver and systemic venous circulation.
Changes at Birth
Clamping of the umbilical cord eliminates placental blood flow through the umbilical vein.
The vessel rapidly becomes functionally inactive and subsequently undergoes fibrous obliteration.
Functional Closure
When placental circulation ceases, pressure and flow within the umbilical vein fall abruptly.
The vessel collapses and progressively closes.
Ligamentum Teres Hepatis
The intra-abdominal portion of the umbilical vein becomes the ligamentum teres hepatis, also called the round ligament of the liver.
This fibrous cord extends from the umbilicus toward the liver within the free margin of the falciform ligament.
Adult Location of the Remnant
The ligamentum teres lies in the free inferior margin of the falciform ligament and continues toward the visceral surface of the liver.
Its position marks the course of the fetal umbilical vein.
Umbilical Vein and Ductus Venosus Remnants
| Fetal Vessel | Adult Remnant |
|---|---|
| Umbilical vein | Ligamentum teres hepatis |
| Ductus venosus | Ligamentum venosum |
Relationship Between the Two Remnants
The ligamentum teres and ligamentum venosum represent sequential portions of the former fetal pathway carrying placental blood through the liver.
Together, they provide visible adult landmarks of the fetal umbilical venous circulation.
Recanalization of the Umbilical Vein
In portal hypertension, paraumbilical veins associated with the region of the ligamentum teres can enlarge and create prominent portosystemic collateral pathways.
This is sometimes described clinically as recanalization of the umbilical vein, although the vascular channels involved may include enlarged paraumbilical veins rather than simple reopening of the original fetal lumen.
Paraumbilical Veins
Paraumbilical veins connect the portal venous system near the liver with veins of the anterior abdominal wall.
They can become enlarged when portal venous pressure rises substantially.
Caput Medusae
Marked dilation of superficial veins radiating from the umbilical region is called caput medusae.
It can occur when portal hypertension produces increased flow through paraumbilical portosystemic collateral pathways.
Umbilical Venous Catheterization
In neonatal medicine, the umbilical vein can provide temporary vascular access shortly after birth.
An umbilical venous catheter may be advanced through the umbilical vein toward the central venous circulation when clinically indicated.
Course of an Umbilical Venous Catheter
A catheter inserted through the umbilical vein follows the fetal venous pathway from the umbilicus toward the liver.
It may pass through the ductus venosus toward the inferior vena cava and right atrial region, depending on the desired catheter position.
Importance of Catheter Position
Correct catheter positioning is important because malposition can place the catheter within hepatic or portal venous branches rather than the intended central venous location.
Imaging is therefore used to confirm appropriate placement according to clinical protocols.
Umbilical Vein Doppler
Ultrasound and Doppler techniques can visualize blood flow within the fetal umbilical vein.
Normal venous flow is generally directed continuously from the placenta toward the fetus.
Umbilical Vein Pulsations
Abnormal pulsatility within the umbilical vein can occur in association with altered fetal central venous pressure or cardiovascular compromise.
Such findings are interpreted with other fetal Doppler measurements and the complete clinical assessment.
Persistent Right Umbilical Vein
A persistent right umbilical vein is a developmental variation in which the right umbilical vein persists rather than regressing in the usual pattern.
Its significance depends on the specific venous anatomy and whether other fetal abnormalities are present.
Umbilical Vein Varix
An umbilical vein varix is a focal dilation of the umbilical vein, often involving its intra-abdominal portion.
Prenatal ultrasound can identify the dilation and evaluate associated blood flow.
Comparison With the Umbilical Arteries
| Feature | Umbilical Vein | Umbilical Arteries |
|---|---|---|
| Normal number | One | Two |
| Direction | Placenta → Fetus | Fetus → Placenta |
| Relative oxygen content | Higher | Lower |
| Fetal abdominal relationship | Courses from umbilicus toward liver | Course from pelvic circulation toward umbilicus |
| Major adult remnant | Ligamentum teres hepatis | Medial umbilical ligaments distally |
Umbilical Vein Blood Sampling
Blood from the umbilical vein can be analyzed after delivery as part of cord blood assessment.
Because the vein carries blood from the placenta toward the fetus, its gas and acid-base values differ from those of paired umbilical arterial blood.
Umbilical Venous Versus Arterial Blood
Umbilical venous blood generally has a higher oxygen concentration and lower carbon dioxide concentration than umbilical arterial blood.
Paired analysis can provide information about placental exchange and fetal acid-base status around the time of birth.
Clinical Importance of the Umbilical Vein
The umbilical vein is important in prenatal imaging, neonatal vascular access, fetal circulation assessment, and understanding adult hepatic anatomy.
Its postnatal remnant also serves as a landmark on the visceral and anterior aspects of the liver.
Key Features of the Umbilical Vein
| Feature | Key Point |
|---|---|
| Normal number | One |
| Developmental origin | Persistent left umbilical vein |
| Direction of flow | Placenta → Fetus |
| Blood carried | Relatively oxygenated, nutrient-rich placental blood |
| Abdominal course | Umbilicus toward fetal liver |
| Major fetal connection | Hepatic circulation and ductus venosus |
| Postnatal remnant | Ligamentum teres hepatis |
Anatomical and Physiological Importance
The umbilical vein is the principal vessel delivering oxygen and nutrients from the placenta into the fetal circulation. Its unusual oxygen content illustrates that veins are defined by the direction of blood flow toward the heart, rather than by whether their blood is oxygenated or deoxygenated.
Its course through the fetal liver is also central to understanding fetal circulatory anatomy. Blood arriving through the vein is divided between hepatic perfusion and the ductus venosus, allowing both the developing liver and the central circulation to receive placental blood.
After birth, the vessel loses its circulatory function but remains anatomically recognizable as the ligamentum teres hepatis. The umbilical vein therefore links placental physiology, fetal cardiovascular anatomy, hepatic development, neonatal vascular access, and adult liver landmarks.
Published on October 1, 2026
Last updated on October 1, 2026
Last updated on October 1, 2026