Babies exposed to certain infections shortly before and after birth have a greater risk of cerebral palsy, Australian research suggests.
The team found viral infections were common in newborns
Scientists tested over 1,300 babies, including 443 with cerebral palsy, for viruses, including the herpes group B virus, which can cross the placenta.
The British Medical Journal study showed the cerebral palsy risk doubled with exposure to herpes group B virus.
Cerebral palsy can cause physical impairments and mobility problems.
It results from the failure of a part of the brain to develop before birth or in early childhood or brain damage and affects one in 400 births.
The team from the Adelaide Women's and Children's Hospital found exposure to viral infections was common in all newborns - especially if they were born premature.
This implied infections before birth may also be linked to pre-term delivery, the researchers said.
But the team concluded only exposure to the herpes B virus, which causes chicken pox and shingles, seemed to be linked with cerebral palsy.
A different herpes virus, group A, causes common cold sores and genital herpes.
However, the researchers added that other factors such as growth restriction, clinical events and genetic susceptibility to infections could be a factor and plan to look at these in further research.
Gary Birkenhead, policy and research officer at cerebral palsy charity Scope, said his organisation would be following any future research with interest.
He said: "Whilst the link between neurotropic virus infection (those which pass across the placenta) and cerebral palsy has been discussed for many years, it is good to see it confirmed in this study from Adelaide.
"As exposure to viral infection was common in all newborn babies, but not all babies developed cerebral palsy, we would very much support further studies that investigate the possible causes of this link."
Mr Richard Warren of the Royal College of Obstetricians and Gynaecologists, said the study supported previous beliefs that antenatal events including some infections may cause cerebral palsy.
"Viral infections are of course common and are often difficult to avoid throughout the nine months of pregnancy.
"But the majority of infections and illnesses, however, are thought not to give rise to harm to the baby," he added.