Within a few minutes of birth, the cord stops pulsing and blood flow ceases.
Evolutionarily speaking, women probably gave birth squatting, a position that would have helped the cord blood to rush toward the baby in the moments after birth, Sanberg said.
Birthing practices, of course, have changed for most U.S. women, and so have ideas about cord blood. Decades ago, doctors also believed the blood inside the cord was ordinary blood, Sanberg noted. Doctors now know umbilical cord blood contains stem cells.
"If you look at most historical societies, babies were born using gravity, which seems to help the transfer of the blood," Sanberg explained. "It's only in the last century that Western medicine has focused on clamping and cutting the cord to separate the baby so quickly."
Clamping cuts off blood supply prior to cutting the cord.
In the 1980s, ob-gyns were taught to clamp the umbilical cord of preterm infants quickly, said Dr. Bruce Young, a professor of obstetrics and gynecology at NYU Langone Medical Center.
Preterm infants are at higher risk of jaundice because they don't yet have a mature enough liver to break down bilirubin, a by-product of red blood cell metabolism. Preventing preterm infants from receiving that extra volume of blood from the mom was believed to help ward off jaundice, Young explained.
But as methods of caring for preemies improved, and doctors learned that exposing infants to light can help with bilirubin metabolism, early cord clamping was no longer encouraged, Young said.
In his experience, Young said, few doctors cut the cord in under a minute, even for full-term newborns. And many of today's moms request to have the baby placed on their abdomen be
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