IVF success rates will fall by up to 20 per cent because of a government policy designed to cut the number of damaging twin pregnancies, research has suggested.

An initiative to limit multiple births by persuading IVF patients to use only one embryo at a time will cause a “significant reduction in treatment success”, according to an analysis of a clinic’s patients.

The Human Fertilisation and Embryology Authority strategy, which aims to cut the twin birthrate by 2012 from one in four to one in ten, would in practice reduce the IVF success rate at St Mary’s Hospital in Manchester from 21 per cent to 17 per cent, the study found.

Daniel Brison, of the University of Manchester, said that the strategy was right to encourage single-embryo transfer because a multiple birth was the greatest IVF risk to mothers and babies, but its implementation needed to be backed by better NHS access to IVF, especially for follow-up courses using frozen embryos.

Evidence from Scandinavia and King’s College London has indicated that some women’s chances of conceiving are just as high with one embryo as with two, if a second frozen-embryo cycle is available.

About a third of NHS trusts do not offer frozen back-up treatment and 85 per cent do not provide the three full cycles that the National Institute for Health and Clinical Excellence recommends.

“Single-embryo transfer is the right way forward, but we have to fund more than one cycle,” Dr Brison said. “It is very difficult to ask patients to accept any reduction in success rates if they have only one shot. Embryo freezing is also crucial, as is careful selection of patients who are suitable for a single embryo.”

IVF produces a higher rate of twins and triplets because multiple embryos are often used to maximise the chances of pregnancy. Such babies, however, are more likely to be stillborn, die in their first year, suffer disabilities or be born prematurely. There are also risks to mothers.

In the study, published in the journal Human Reproduction, Dr Brison and his colleagues Stephen Roberts and Cheryl Fitzgerald constructed a model of what would happen to their clinic’s success rates under the single-embryo strategy.

To achieve the target of 10 per cent multiple births, about 55 per cent of patients would have to have single-embryo transfer. The current rate is about 10 per cent. This would bring the success rate down by about 20 per cent. If women were selected carefully, the decline would be slightly smaller but the live birthrate would still fall to 18.5 per cent.

The paper suggests ways that women could be selected, including analysis of their embryos as well as their age and hormone levels. Such measures would be essential to limit the policy’s impact on pregnancy success, the scientists said.

The St Mary’s success rate is below the national average of 31 per cent for women under 35 who use their own fresh eggs. It is an NHS centre with a waiting list of up to three years, so couples with a good prognosis often conceive spontaneously while waiting for treatment, leaving the clinic to treat harder cases.

Professor Peter Braude, of King’s College London, led the group that drew up the single-embryo strategy. He said that patients could be chosen who would not be disadvantaged by the policy.

“It doesn’t reduce pregnancy rates in women who are most likely to get pregnant, and who are also most likely to have twins,” he said.

“We have never said that a single embryo is right for every woman and the 10 per cent target is an aspiration. A very small proportion of patients give rise to most of the twins and by identifying them, we can reduce multiple births but not the pregnancy rate.”

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