The yolk sac and the allantois give rise to and are preserved in the umbilical cord. By the fifth week of development, it has formed and is the embryo's new source of nutrition, taking the place of the yolk sac. The cord joins the placenta, which transports substances to and from the mother's blood without allowing them to directly mix, rather than being directly attached to the mother's circulatory system. The umbilical cord can be clamped at various times, although postponing it until at least one minute after delivery improves results, provided that the minor risk of jaundice can be treated if it does occur. Clamping is followed by a painless cord cutting procedure because there are no nerves present. Out of those 20 studies, only 5 studies discuss the risk associated with delayed cord clamping, 2 studies discuss the benefit associated with good nutritional status, 2 studies discuss the benefit associated with good neurodevelopment, and the remaining studies discuss the increase in hemoglobin due to delayed cord clamping.