<P> It is unusual for a vein to carry oxygenated blood and for arteries to carry deoxygenated blood (the only other examples being the pulmonary veins and arteries, connecting the lungs to the heart). However, this naming convention reflects the fact that the umbilical vein carries blood towards the fetus's heart, while the umbilical arteries carry blood away . </P> <P> The blood flow through the umbilical cord is approximately 35 ml / min at 20 weeks, and 240 ml / min at 40 weeks of gestation . Adapted to the weight of the fetus, this corresponds to 115 ml / min / kg at 20 weeks and 64 ml / min / kg at 40 weeks . </P> <P> The umbilical cord enters the fetus via the abdomen, at the point which (after separation) will become the umbilicus (or navel). Within the fetus, the umbilical vein continues towards the transverse fissure of the liver, where it splits into two . One of these branches joins with the hepatic portal vein (connecting to its left branch), which carries blood into the liver . The second branch (known as the ductus venosus) bypasses the liver and flows into the inferior vena cava, which carries blood towards the heart . The two umbilical arteries branch from the internal iliac arteries, and pass on either side of the urinary bladder into the umbilical cord, completing the circuit back to the placenta . </P> <P> In absence of external interventions, the umbilical cord occludes physiologically shortly after birth, explained both by a swelling and collapse of Wharton's jelly in response to a reduction in temperature and by vasoconstriction of the blood vessels by smooth muscle contraction . In effect, a natural clamp is created, halting the flow of blood . In air at 18 ° C, this physiological clamping will take three minutes or less . In water birth, where the water temperature is close to body temperature, normal pulsation can be 5 minutes and longer . </P>

Where is the umbilical cord attached to the baby