Though bleeding may occur in the brains of as many as one out of four infants born vaginally, it is unlikely to cause adverse consequences. Most bleeds detected in a recent study were very small and resolved on their own.

"Small bleeds in and around the brain are very common in infants who are born vaginally," said John H. Gilmore, MD, professor of psychiatry and vice-chair for research and scientific affairs at the University of North Carolina School of Medicine in Chapel Hill. "It seems that a normal vaginal birth can cause these small bleeds."

Intracranial hemorrhages, or ICH, were significantly associated with vaginal birth, but they were not dependent on prolonged duration of labor or on traumatic or assisted vaginal birth.

"In our study, neither the size of the baby or the baby's head, the length of the labor, nor the use of vacuum or forceps to assist the delivery caused the bleeds," Dr. Gilmore said. "The bleeds are probably caused by pressure on the skull during delivery."

Most of the bleeds identified were very small. Typically, small bleeds resolve over time without permanent effects, though larger ones may cause seizures, subtle learning problems, difficulties with motor development, or other problems later in life.