Researchers in the United States have found that many babies who were delivered vaginally, experience bleeding in and around the brain shortly after birth.
They have discovered this by using magnetic resonance imaging (MRI) for the first time to look at the brains of babies soon after they were born.
The researchers from the University of North Carolina School of Medicine in Chapel Hill say the bleeding occurred in as many as one in four babies and is very common in infants who experience a normal vaginal birth.
The researchers examined 88 newborns, with equal numbers of boys and girls, at an average of two weeks after birth.
Sixty five were delivered vaginally and 23 by cesarean section, in which the baby is surgically delivered through the mother's abdomen.
Of the 65 delivered vaginally, 17 babies (26 percent) had bleeding in and around the brain, called intracranial hemorrhages, mostly in the lower, rear part of the brain.
None of the C-section babies had this bleeding.
Dr. John H. Gilmore, a professor of psychiatry and Vice-Chair for Research and Scientific Affairs at the University, says the bleeding did not appear to be associated on the length of the labour, the size of the baby's head, or whether it was a difficult or assisted vaginal birth, where a vacuum or forceps were used to assist the delivery.
As the bones of the skull in newborns have not fused together they are able to shift and often overlap each other during vaginal delivery, in order for the baby's head to pass through the birth canal.
This process can compress the brain or cause blood vessels to tear, which causes bleeding called subdural hematomas most of which are apparently very small and cause few problems.
Larger ones can cause problems later in the child's life, such as seizures, learning problems or problems with motor development.
Dr. Gilmore says it is unclear at present what the long term effects of larger bleeds are and more research needs to be done in this area.
Gilmore adds that the study should in no way influence parents against vaginal delivery and act as an endorsement of C-sections, as the vast majority of people were born vaginally and may have had such bleeds and suffer no long term problems.
The researchers will examine the children again at ages 1 and 2 in order to see if they have any enduring problems.
The study appears in the February issue of Radiology.