Umbilical cords cut too soon.

Or if you're Jewish like me, it's never cut. From Live Science:

Usually within the first minute of birth, the umbilical cord running between mother and infant is clamped. But this may be too fast, researchers say.

Waiting until the cord stops pulsing could give the newborn significant health benefits, suggests a review article in the most recent issue of the Journal of Cellular and Molecular Medicine.

"Ob-gyns and parents should think about giving the cord blood to the baby," said lead researcher Paul Sanberg of the University of South Florida. "It only takes a few minutes."

The umbilical cord carries nutrients and oxygen from mom-to-be's placenta to the developing infant's abdomen. (It leaves a life-long impression in the form of the belly button.) When the practice of immediate cord clamping first began about a half century ago, the value of cord blood, especially its stem cells, which can develop into a suite of other cells, was not known. But now we know that stem cells have many therapeutic properties, Sanberg told LiveScience.

"It is not just regular blood going in," he said. "It is nature's first stem cell transplant."

Common problems in newborns are usually related to their underdeveloped organs, which might be helped by the regenerative properties of stem cells, Sanberg theorized.

After reviewing the majority of research in the field, Sanberg and his colleagues concluded that delaying cord clamping could reduce the infant's risk of many illnesses, including respiratory distress, chronic lung disease, brain hemorrhages, anemia, sepsis and eye disease.

The risk of such problems, and thus the potential benefit of delaying cord clamping, is particularly significant for premature babies and those born malnourished or suffering from other complications.