It is standard practice when babies are born to clamp the umbilical cord immediately and then cut between the clamps, severing the connection between mother and infant in the first minute after birth. It has been done that way for decades, in part because it was believed that doing so reduces the risk of hemorrhage in the mother.
Recent evidence suggests that it may be better to delay cutting the cord for a minute or two after birth. After reviewing the outcomes of more than 3,900 women-infant pairs in 15 different previous studies, the authors of a recent study concluded that delaying cutting the cord did not increase the risk of maternal hemorrhage significantly. On the other hand, delaying cutting the cord for just several minutes resulted in improvement in several measures of infant health; a higher birth weight, a higher hemoglobin concentration several days after birth, and a reduced likelihood of iron deficiency at 3-6 months. The only negative was that delaying cutting the cord slightly increased the tendency for jaundice in the infant. Overall, the results suggest that in many normal deliveries, delaying clamping the cord for just a minute or two is probably beneficial overall.
Why would delaying cord clamping for such a short time be beneficial? The most likely explanation is that immediately after delivery the rate of cord blood outflow from the infant declines relative to inflow to the infant. So in that first minute or two, the infant gains a significant amount of blood from the mother in preparation for an independent life. Estimates are that the infant may receive as much as a third of its blood supply in that crucial first minute or two after birth.