Treatment success: Annie Greenhouse with her nine-month-old son Finlay

Thousands of women could be spared the misery of repeated miscarriages with a pill that costs just £1 a month, it emerged yesterday.

Researchers have found fresh evidence that a third of unexplained miscarriages may be caused by an overactive immune system.

They believe treatment with a common steroid, used for asthma and allergies, can curb the immune response and protect an unborn baby in the crucial early weeks of pregnancy.

The findings offer hope to around 9,000 women who have unexplained miscarriages each year in Britain.

In preliminary trials, around three-quarters of women who had a history of miscarriages had successful pregnancies after taking the steroid.

Dr Siobhan Quenby, who is carrying out the pioneering work at Liverpool University, is now beginning a larger trial to make sure the results are not simply down to the placebo effect.

She also hopes to develop a test that could screen women for miscarriage risk before they become pregnant.

This would replace the barrage of up to 30 blood tests that patients currently undergo to determine what may have caused them to lose their baby.

‘It is a matter of life and death,’ Dr Quenby said. ‘There are thousands of people who are desperate because they keep miscarrying and there’s no treatment. I am inundated with emails from women and there is a massive, desperate need.’

Dr Quenby has previously shown that a third of women who suffer recurrent miscarriages have an abnormally high number of ‘natural killer’ cells in their uterus. These cells – which are part of the body’s natural armoury – roam the body destroying viruses and infected cells.

They are also involved in the creation of new blood vessels. In the latest study, Dr Quenby took biopsy samples from 120 women who had suffered repeated miscarriages.

She found high levels of NK cells increased the number of blood vessels in the uterus in the early stages of pregnancy.

These blood vessels increase the amount of oxygen in the womb – at a time when a newly conceived embryo needs low levels to implant itself in the womb lining.

By giving pregnant women prednisolone, Dr Quenby believes she can reduce oxygen levels and increase the chances of a baby surviving.

In early trials of the drug, 30 out of 40 women suffering from repeated miscarriages, who also had high NK levels, went on to have successful pregnancies. One had suffered 22 miscarriages.

In a new trial which began last month, Dr Quenby plans to test these results by giving half of the women she recruits a dummy placebo and the rest a dose of the steroid.

Prednisolone’s side effects include mood swings and increased appetite.

However, most women would need to take it for just three months.

Professor Susan Wray of Liverpool University said: ‘There’s real hope that in five to ten years this could have a significant impact. It’s really terrific.’

The baby I always longed for

After her fourth miscarriage in as many years, Annie Greenhouse, pictured above, was about to give up.

Despite desperately wanting a family, she and her 38-year-old husband Mark, a management consultant, felt unable to go through the pain of another lost baby.

‘I was absolutely devastated the first time I miscarried, and it got harder each time,’ she said.

‘After the fourth one I felt “that’s it, I can’t possibly do this".’

Doctors told her there was nothing they could do.

But after reading about the pioneering research at Liverpool on the internet, the couple travelled from their York home to meet Dr Siobhan Quenby.

Within months Mrs Greenhouse, 35, was pregnant. Tests in December 2006 had revealed she had high levels of natural killer cells and she was put on daily doses of prednisolone.

The couple are now the proud parents of nine-month-old Finlay.

The pregnancy was an anxious time for the couple but they were overjoyed by the long-awaited birth.

‘I would try for more without a shadow of a doubt,’ Mrs Greenhouse said. ‘And I’m confident it was the treatment, I felt different in myself.’