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 issues, and infections. In 1958, James L.S. recognised that umbilical cord blood gas analysis can give an indication of preceding fetal hypoxic stress. It has since become widely accepted that umbilical cord blood gas analysis can provide important information about the past, present and possibly the future condition of the infant. PUBS dates back to 1964 when Freda and Adamsons reported the removal of a uterus containing a fetus who had a buildup of fluid and ended up dying; however, this was one of the first procedures that showed promise for current day PUBS. Valenti hypothesized in 1972 that the