Birthweight has an influence on cerebral palsy risk

Major research into affected babies, published in the Lancet journal, has concluded that disasters at birth cause only a fraction of cases.

Experts from Newcastle and Liverpool believe that infections and blood defects in pregnancy could be blamed.

Both low, and high birthweight babies were at increased risk, they found.

The researchers believe that even a "vanishing twin" - in which two embryos implant, but one foetus dies and disappears during pregnancy, may increase the chances of the surviving "twin" developing cerebral palsy.

Common disability

The term cerebral palsy covers a wide range of physical problems in which poor brain development or damage has affected the ability to control muscle and movement.

It is the most common cause of severe physical disability in children in developed countries.

The cause of the condition is still poorly understood - although some cases are linked to difficult births in which the oxygen supply to the baby's brain is cut off at a critical moment.

Cases in which this is due to a mistake by obstetric staff have led to large sums being paid in compensation to help pay for care.

In order to probe the reasons behind the problem, Dr Stephen Jarvis, from the University of Newcastle, looked at data in registers of cerebral palsy children in 10 different European countries - approximately 4,500 in total.

The birthweight and other pregnancy details in each case were scrutinised for common factors that might point to a cause.

They found that the smallest 10% of babies were four to six times more likely to develop cerebral palsy - while those in the top 3% had a three-fold increased risk.

'Surprising

Dr Mario Peterson, from the University of Tennessee Health Science Center in Memphis, said that the finding that bigger babies were more at risk was "surprising".

He said that this could not be explained away by the fact that large babies tended to be prone to more complications during delivery.

He said: "The abnormal or injured brain could lead to accelerated growth through neuroendocrine or other central influences.