Minor brain hemorrhages occur in as many as one in four otherwise healthy newborns -- a finding that surprised researchers at UNC-Chapel Hill and could help physicians avoid wrongly accusing parents and caregivers of child abuse.

The researchers, whose findings appear in the February issue of the journal Radiology, note that bleeding in an infant's brain is commonly associated with "shaken baby syndrome," a traumatic brain injury that occurs when an infant is violently shaken. Intracranial bleeding, which can cause serious brain damage or even death, is a hallmark characteristics of a shaken baby.

That's why physicians at UNC-CH were taken aback at results they collected during a radiology study looking into early brain development. Scan after scan of infants turned up brain bleeds. Twenty-six percent of babies delivered vaginally scanned with supersensitive magnetic resonance imaging, or MRI, showed evidence of such bleeding. Previous studies have found brain bleeds at significantly lower rates. Bleeding was less common in babies delivered by cesarean section.

Dr. J. Keith Smith, a UNC-CH radiologist who specializes in brain imaging, said physicians in his field are trained to suspect child abuse when they see intercranial bleeding. But as the bleeds showed up in more and more babies, and those children showed none of the classic signs of brain injury, Smith and his colleagues concluded that minor bleeding might be relatively common. Smith, a co-author of the Radiology article, speculates that newer, more sensitive imaging technology has only recently made it possible for doctors to see it.

"It's probably something that has always been there," he said.

Researchers think that bleeding in vaginally delivered babies occurs as the infant's still-flexible skull is compressed while passing through the birth canal. UNC-CH physicians noted that the hemorrhages they observed tended to be tiny and concentrated near the back of the brain. By contrast, bleeding associated with shaken baby syndrome tends to cover a larger area and is most often found at the top of the brain.

Those distinctions might help physicians rule out child abuse when they see minor intercranial bleeding, Smith said.

Doctors don't have enough information to say whether the minor, birth-related bleeding is harmful, though they suspect not. Small bleeds typically resolve on their own, but larger ones might cause lingering effects, including problems with motor development.

"Obviously, the vast majority of us who were born vaginally and may have had these types of bleeds are doing just fine," said Dr. John H. Gilmore, a UNC-CH psychiatrist and co-author of the Radiology paper. "Humans have been born vaginally for a very long time, and our brains probably evolved to handle vaginal birth without major difficulty."