ANATOMY OF THE UMBILICAL VEIN

• The intra-abdominal portion of the UV ascends steeply from the cord insertion in the inferior part of the falciform ligament. The vessel continues in a more horizontal and posterior direction, turning to the right at the confluence with the transverse part of the left portal vein, which joins the right portal vein (divides into anterior and posterior branches), at the main lobar fissure.

• Sonographically the umbilical vein enters the liver almost midline and passes to the left of the gallbladder.

• No branches in liver (therefore the volume of blood entering the left portal venous system is equal to that in the UV). The fetal left portal vein is larger than the right portal vein (the reverse situation is seen in the child adult).
  If branches are seen then the left portal vein is being scanned and not the umbilical vein.
• 40-60% of umbilical venous flow is to the IVC via the liver and portal veins. The rest of the UV flow is via the ductus venosus to the IVC.
• Size
• 3mm at 15 weeks.
• 8mm at term.