Currently it is published that there is a one way transfusion of 30% (about 100cc) increase in blood volume if the umbilical cord is not cut for a minute after birth. My question is : by what mechanism do you explain the delivery of an extra 100 cc (30% increase in blood volume ) of blood to the fetus shortly after birth?

In other words, how do you explain a one way blood transfusion in the first minute after birth of 100 cc of blood in a 3 kg baby.

In other words : how does the newborn direct the cord which until then was functioning as a two way tool to circulate blood in two directions, in and out, to suddenly function in one direction only, i.e. into the fetus, with no blood returning to the cord, but rather only delivering blood from the now detached placenta to the newborn ?

The research says the uterus contracts after birth pushing the cord blood into the newborn. But there aren't uterine contractions in the first minute after birth and if there were, it would encourage blood to flow in two directions.