Women whose hopes of having a baby are repeatedly thwarted by miscarriages may be helped by a common steroid drug that is normally used to manage conditions such as asthma and eczema.

Preliminary studies by researchers at Liverpool University indicate that the highest success rate is likely to be among those who take prednisolone over three successive menstrual cycles before pregnancy.

Of 29 volunteers who took the drug in a test, seven became pregnant. Two of them miscarried, two had healthy babies and three have been pregnant for longer than three months, the period in which miscarriages usually occur.

The women involved had previously had between three and 22 miscarriages each. Now the team hopes to recruit up to 700 such women to put the drug to a wider controlled test.

The Liverpool team, headed by Siobhan Quenby, believes the problem may be caused by the fact that some women have too many of what are called uterine natural killer cells, white blood cells in the womb lining.

The theory, which is not accepted by all in the fertility world, is that these sometimes interact badly with cells in the foetal placenta.

These uterine natural killer cells have positive benefits, for instance, in fighting cancers and viruses, but too many of them may create an imbalance which leads to miscarriage.

The trial involving 29 women followed success in treating a 42-year-old woman who had 19 miscarriages, but was given prednisolone and now has a two-year-old child.

Dr Quenby, who gave details of her work to a fertility conference in Copenhagen yesterday, said the drug would not work with everyone. But the findings so far might lead to new ways of combating a condition for which no satisfactory treatment exists.

"It is an exciting step in the right direction ... but it doesn't prove all these women are going to go on to have babies."

In a presentation to the conference today, a paediatrician, Alastair Sutcliffe, of University College, London, will warn that parents who undergo fertility treatment are at up to 10 times more risk of having babies with a rare condition called Beckwith-Widermann syndrome. This occurs in between one in 12,000 and one in 15,000 births.

Such babies are often premature, but are heavy and tall. They sometimes have enlarged tongues, jutting jaws, and, in more serious cases, kidney tumours. The condition can usually be treated by drugs and diet, with surgery sometimes being necessary.