A good article illustrating the potential negative effects on the newborn child's brain of prematurely cutting the umbilical cord after birth is Brain Damage by Asphyxia at Birth by William F. Windle (Scientific American, Volume 221, Number 4, October 1969).
The practices outlined in this article, including clamping the umbilical cord immediately after birth, are still routine in many hospitals today. The author recommends in the article that the umbilical cord remain intact until the placenta is delivered to ensure the infant does not lose all the fetal blood still in the cord. If you plan on having your baby in the hospital, you should do some research on why it is potentially dangerous and harmful to have the umbilical cord cut within seconds of your baby’s birth. I always cringe when I see the cord cut immediately after birth.
Unassisted birthers wait for nature to take its course. It’s not uncommon for the placenta to detach twenty minutes, forty-five minutes, an hour or even a few hours after the baby is born. Many women cut the cord after the placenta’s out, while others opt for a “lotus birth.”