Brain haemorrhages in babies over a month old are unlikely to be caused by problem births, researchers say.
Difficult deliveries are sometimes cited as a defence in child abuse cases where a baby has a brain injury.
But a team from the Royal Hallamshire Hospital in Sheffield have found this is unlikely to be the case unless the baby is very young.
Their study in the Lancet showed bleeds caused by birth problems healed by the time the baby was four weeks old.
This suggests that injuries in older babies are unlikely to be anything to do with the birthing process.
Experts said this kind of bleed in the brain could be caused by a blow to the head, although a baby which had been shaken would be more likely to have general brain swelling.
The Sheffield researchers looked at 111 babies. Magnetic resonance imaging (MRI) scans of their brains showed nine suffered internal bleeds, known as subdural haematomas, at birth.
The researchers said this was a higher incidence than had previously been estimated.
But further scans at four weeks, six months and two years of age, showed the bleeds had healed by the time the babies were a month old, and caused no further problems.
Five of the babies were delivered using forceps after an attempted ventouse delivery, three were normal vaginal deliveries and one had a traumatic ventouse delivery.
None of the babies needed treatment for their bleeds.
The researchers said larger studies were needed to confirm their findings.
Dr Elspeth Whitby told BBC News Online: “We wanted to find out more about the delivery process.
“Did that cause bleeds, and if so, what type of delivery caused them?”
She added: “This study is important from the aspect of non-accidental Head injury.
“In a court of law, the defence may claim that an isolated subdural haemorrhage presenting in later infancy is due to a birth injury.”
But she said the bleeds appeared to be harmless, did not cause any symtoms, and seemed to cause no long-term problems.
Dr Harvey Marcovitch of the Royal College of Paediatrics and Child Health told BBC News Online the research was important because it would help doctors work out how a baby’s brain bleed had been caused.
“We were uncertain about how long the signs stayed for.
“This research is very helpful because if you find something in a baby over a month old, it does suggest you can discard birth injury as an explanation.”
He added: “I have heard this used as a defence in legal cases.”
But Dr Marcovitch said more research was needed.
“This study covers a disappointingly small number. But it can be seen as a pointer.”
Revision date: June 14, 2011
Last revised: by Andrew G. Epstein, M.D.