Overview

Length at term≈50–60 cm

Vessels2 arteries + 1 vein

The umbilical cord forms from the connecting stalk as the expanding amnion envelops the yolk-sac stalk and allantois. At term it is about 50–60 cm long and 1–2 cm thick, typically spirally twisted. It contains two umbilical arteries, branches of the fetal internal iliac arteries, which carry deoxygenated blood to the placenta, and one umbilical vein (the persisting left vein), which carries oxygenated, nutrient-rich blood back to the fetus — most of which bypasses the liver via the ductus venosus into the inferior vena cava. The vessels are cushioned in Wharton's jelly, a mucoid connective tissue rich in hyaluronan that resists compression and kinking. The cord lacks nerves; vessel tone is controlled locally.

After birth, the vessels constrict and close. Their remnants are: umbilical vein → ligamentum teres hepatis (round ligament of the liver); ductus venosus → ligamentum venosum; distal umbilical arteries → medial umbilical ligaments (proximal parts remain as the superior vesical arteries); and the allantois/urachus → median umbilical ligament.

Location: From the fetal umbilicus to the fetal surface of the placenta (usually inserting near its centre).

Parts & subdivisions

Umbilical arteries (2)
Carry deoxygenated fetal blood to the placenta.
Umbilical vein (1)
Carries oxygenated blood to the fetus.
Wharton's jelly
Mucoid connective tissue protecting the vessels; source of mesenchymal stem cells.
Amniotic covering
Outer epithelium continuous with the amnion.

Function

Conveys fetal blood to and from the placenta.

Clinical significance

Single umbilical artery

Found in ≈0.5–1 % of cords; associated with fetal renal and cardiac anomalies, aneuploidy and growth restriction — prompts a detailed anomaly scan.

Cord emergencies

Cord prolapse after membrane rupture (especially with malpresentation) compresses the vessels — an obstetric emergency requiring immediate delivery. Vasa praevia — unprotected fetal vessels (velamentous insertion) crossing the internal os — can rupture and exsanguinate the fetus.

Neonatal practice

Delayed cord clamping (≥1 min) improves infant iron stores; cord blood gases assess intrapartum hypoxia; the umbilical vein is used for emergency neonatal venous access; cord blood can be banked for haematopoietic stem cells.

Test yourself

How many vessels does the normal umbilical cord contain?

One artery and one vein
Two arteries and one vein
One artery and two veins
Two arteries and two veins

Answer: Two arteries and one vein

Two umbilical arteries carry deoxygenated blood from the fetus to the placenta; one umbilical vein returns oxygenated blood. A single umbilical artery is associated with renal and cardiac anomalies.