The Oracle study found babies had a greater risk of developing the disability if their mothers' waters had not broken and they were given antibiotics despite showing no signs of infection.

The Medical Research Council (MRC) report found the risk was not greater where mothers had gone into premature labour and their waters had broken.

The trial took place between July 1994 and May 2000 in 161 hospitals worldwide involving 11,050 women. The majority of research was carried out in the UK, with trials in 135 hospitals.

Some women in the trial gave birth to children three times more likely to develop cerebral palsy, although the risk was still low.

Across Yorkshire 14 hospitals were involved in the trial, including Bradford Royal Infirmary, Huddersfield Royal Infirmary, Leeds General Infirmary and the Friarage Hospital in Northallerton.

The study was set up to find out if giving antibiotics would improve a baby's chance of survival. Two types of antibiotics were given to women who either had broken waters or were threatening premature labour. Although the original trial found that the drugs produced no adverse effects, a recent follow-up has discovered that women who were given the drugs gave birth to children with a higher risk of developing cerebral palsy or other functional impairments.

Sara Kenyon, from Leicester University, who led the Oracle study, said: "We hoped there would be benefits seen by the trial. As yet, we don't understand why it can have happened.

"Before the trial, there was some evidence of short-term benefits of antibiotics in premature labour, but we did not know what the long-term outcomes would be, which is why we conducted the follow-up."

Dr Catherine Elliott, the head of clinical research support and ethics at the MRC, said: "The results were unexpected and the MRC is considering what further research could shed more light on these findings."

"The MRC want to make it clear that the results of the study do not mean that pregnant women with an infection should not take antibiotics.

"Pregnant women with an infection should always take antibiotics if they are given them. Where there is obvious infection, antibiotics may be life-saving for both mother and baby."