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
Umbilical cord higher rate of neonatal jaundice requiring phototherapy. Delayed clamping is not recommended as a response to cases where the newborn is not breathing well and needs resuscitation. Rather, the recommendation is instead to immediately clamp and cut the cord and perform cardiopulmonary resuscitation. The umbilical cord pulsating is not a guarantee that the baby is receiving enough oxygen. However, where possible, one should perform cardiopulmonary resuscitation with the cord still attached, to receive both benefits of oxygen from the cord and from the intervention. Some parents choose to omit cord severance entirely, a practice called "lotus birth" or umbilical nonseverance.