Umbilical cord from and contains remnants of the yolk sac and allantois. It forms by the fifth week of development, replacing the yolk sac as the source of nutrients for the embryo. The cord is not directly connected to the mother's circulatory system, but instead joins the placenta, which transfers materials to and from the maternal blood without allowing direct mixing. The length of the umbilical cord is approximately equal to the crown-rump length of the fetus throughout pregnancy. The umbilical cord in a full term neonate is usually about 50 centimeters (20 in) long and about 2 centimeters (0.75 in) in
Percutaneous umbilical cord blood sampling are self-resolved within five minutes. The complication of infection has a low incidence rate, and preventative measures are implemented against the risk of infection, such as antibiotic usage and the aseptic technique. However, vertical transmission of a virus such as HIV may occur. Fetal loss may also occur, especially in the presence of several risk factors, including fetal abnormalities, operator errors, placental penetration, and viability of the fetus. Intrahepatic vein fetal blood sampling may be done as an alternative to PUBS. It involves the needle being inserted into the intrahepatic part of the umbilical cord in the fetal abdomen. The