Women who have suffered repeated miscarriages or failed IVF treatment could become mothers by taking a course of steroids, trials have shown.

Up to 3,000 unexplained miscarri-ages, a third of the annual total, might be prevented each year by the drug, the British Association conference in Liverpool was told yesterday. Siobhan Quenby, of the University of Liverpool and the Liverpool Women’s Hospital, said that tests involving 120 women had identified natural killer cells as a cause of miscarriages and failed IVF embryo implants.

Natural killer cells are beneficial in most of the body because they can destroy infected or malignant cells, but in the uterus they have been found to promote rapid growth of blood vessels when present in high numbers. The blood vessels transport additional oxygen-bearing blood and can cause miscarriages or prevent embryos implanting.

Steroids have been given to 40 women by Dr Quenby and three quarters of them have successfully given birth. All had previously had multiple miscarriages.

The treatment has been shown to reduce the level of natural killer cells in the uterus, and this is thought to increase the chances of an embryo going to full term. Dr Quenby said: “There are thousands of people around the world who are desperate because they keep miscarrying, and there’s no cause found and there’s no treatment. I’m inundated with e-mails. There’s a massive, desperate need.”

She said of her research: “If we have higher levels of natural killer cells in the uterus we have more blood vessels and more blood flow. We’ve been able to find a missing piece of the jigsaw of why some women have multiple miscarriages.”

She calculated that a third of miscarriages could be prevented: “I’ve looked at 430 biopsies and it always comes out as about a third have high natural killer-cell levels.”

Steroids were first used as a potential treatment by Dr Quenby when she was looking for ideas to help Annette Quinlan, a psychiatric nurse who had suffered 19 miscarriages in 14 years. Mrs Quinlan had a high level of natural killer cells but after steroids she gave birth in 2003 to a girl, Niamh.

What remains unclear is whether the steroids are directly responsible or whether another factor, such as the placebo effect, could have played a role.

Dr Quenby, in partnership with the Miscarriage Association, is looking for 40 women with high levels of natural killer cells and a history of miscarriages to take part in a trial.

The tests involving a course of prednisolone steroid tablets are designed to establish whether or not the placebo effect was responsible for the successful pregnancies. Even if successful, it is expected to take five to ten years for the approach to be approved.

Lord Winston, a fertility expert, hosted a question-and-answer session with Dr Quenby yesterday. He praised her work but voiced doubts about the role of natural killer cells and steroids.

“The key problem which confronts all these studies is the issue of the placebo effect. I think the evidence on killer cells though interesting is still not a very clear mechanism,” he said.

Annie Greenhouse was given steroids early in her pregnancy when she was found to have high levels of natural killer cells after her fourth miscarriage. Mrs Greenhouse, 35, of York, said: “I had a daily dose of the steroid. You don’t start medication until you are pregnant. You go to hospital and they do a scan at five weeks. If it’s not ectopic, they start,” she said.

Finlay, a healthy boy, was born nine months ago and Mrs Greenhouse is convinced that the steroids were responsible for preventing a miscarriage.

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