A baby whose mother died of CJD might have to wait years to learn if the disease has been transmitted to him, an expert on the disease said yesterday.

Julia Blair, a teacher aged 28, died four months after giving birth to Jonathan. She did not realise she had variant CJD until the end of her pregnancy, attributing her symptoms to carrying a baby.

Professor Hugh Pennington of Aberdeen University, an expert on the spread of diseases, who has studied the human form of BSE for several years, said little research had been done into the possibility of transmission between mother and child, and that more was required. The need to study possible transmission between mother and baby was particularly important, he said, because vCJD was common among people in their late 20s, the time when many women were giving birth.

He said: "We don't know the route of transmission or exactly how transmission takes place and whether the agents get into the placenta. A lot of the work that has been done on the disease is based on older people. We'll have to wait and see how it shows itself in babies. At the moment we simply don't have the lab tests to see what's happening in the early stages of infection."

Professor Pennington added that in his view, it was "less, rather than more likely" the newborn child would become infected, although that was not supported by evidence. "The disease has a long incubation period anyway so it might be a while before it's found out."

Last year doctors feared an 11-month-old girl had contract-ed the disease from her mother while in the womb after her growth rate was found to be half that of a normal child of her age. The child also had poor sight and stiff limbs, although an examination of her appendix for evidence of vCJD proved to be inconclusive.

Research by the Veterinary Laboratory Agency on cattle suggested there was a 10 per cent chance of cows transmitting the disease to their calves.

Mrs Blair was diagnosed with the disease after she had given birth at Southern General Hospital, Glasgow. Her last weeks were spent at a cottage next to the home of her husband's parents in nearby Paisley. Fellow members of the Greenview Evangelical Church in Glasgow were said to be comforting her husband, Nick, 30. Mr Blair, also a teacher, believes his son is not at risk.

The connection between BSE-infected beef and vCJD was established in 1996, seven years after BSE was detected. More than 100 people have died from vCJD in Britain.