By Caroline Ryan
BBC News, Prague
A new embryo test offers couples at risk of serious genetic diseases a greater chance of having an unaffected baby through IVF, UK scientists say.
The test could be offered to more than 100 families a year
The test looks at the whole DNA of a cell rather than focusing on a specific mutation in one gene, making it quicker to identify diseases in embryos.
It also allows doctors to check for many more potential illnesses.
The team will tell a Prague fertility conference five couples are expecting healthy babies after the test, and IVF.
However, some campaigners have questioned the morality of such screening tests, as they inevitably lead to the destruction of some embryos.
Simone Aspis, from the British Council of Disabled People, said: "Who is going to make the decision about who should and should not live? We believe all babies have an equal right to life."
The new "DNA fingerprint" test of a cell can spot from a genetic signature that a condition, such as cystic fibrosis, is present, the scientists behind it say.
The team, from the genetics unit at London's Guy's Hospital, have developed a method called pre-implantation genetic haplotyping (PGH), which they expect to offer to over 100 families a year.
The current test is known as pre-implantation genetic diagnosis (PGD).
PGH involves testing parents and any existing children or relations carrying or with a genetic condition, to identify the faulty units of chromosomal DNA.
Using this information, it is possible to take a cell from the embryo, treat it in the lab to create more copies of its genetic material and then look for markers that show an embryo carries two copies of these faulty units, or haplotypes.
This would mean it would be affected by the condition.
The technique has been used to test for Duchenne Muscular Dystrophy (DMD). It primarily affects boys, who inherit the disease through their mothers.
Families with a history of the condition are currently offered embryo sex testing and no male embryos are implanted, as it is not possible to tell if they have the condition - even though they have a 50/50 chance of being affected.
But with the new test, doctors are able to see if an embryo carries the tell-tale DMD haplotypes seen in its parents, meaning more embryos can be selected for use.
The test also allows detection of any of the genetic mutations which can cause cystic fibrosis.
Like DMD, it is a recessive disease, and means both copies of chromosome 7 must carry a fault for a child to have the disease - but PGD can spot only the most common of the hundreds of faults.
The team have also helped a woman affected by hydatidiform mole - a condition where pregnancy leads to a potentially fatal tumour forming instead of a foetus.
Professor Peter Braude, the fertility specialist who helped develop the test, said: "It doesn't matter what the genetic fault is.
"We can know the same chromosome that has affected a family member, and know the embryo is also affected."
Alison Lockwood, a nurse who is part of the genetics unit team, said the bottom line for couples who came to see her was the wish for a healthy baby.
"Until now, you really had to know the name of the mutation to do a direct test. Now that doesn't matter.
"With sex linked disease, you would currently have to take away probably 50% of embryos because they are male.
"But with this test, you might get up to 75% of embryos for transfer."
However she said the new test would not lead to a flood of people wanting to take advantage of the science.
"Of the patients currently referred for PGD, only a third end up going through a cycle.
"These are, generally, couples who can get pregnant without having to undergo fertility treatment, and when they get to know what it involves, many do not go ahead."
Dr Mark Hamilton, chairman of the British Fertility Society, said: "Any technique which has the potential to reduce the risk of serious, debilitating and potentially life-threatening disease has to be greeted with some enthusiasm.
"We are always striving to maximise the chance that fertility treatment will be successful.
"But not transferring because we are absolutely confident they are affected by a condition, rather than because we suspect they are, is preferable and much less wasteful."
But Josephine Quintavalle, of Comment on Reproductive Ethics, warned against further extensions of screening.
She said: "I am horrified to think of these people sitting in judgment on these embryos and saying who should live and who should die."