People who carry the genes for cystic fibrosis will have an alternative way to avoid their children being born with the debilitating condition, fertility specialists have said.

Current tests on unborn children give parents the harsh choice between giving birth to a child with cystic fibrosis or having an abortion, they said.

But a technique that uses test-tube baby procedures has now been developed to identify the disease in most cases before an embryo is placed in the womb.

As is normal in test-tube pregnancies, a number of embryos are created. When the embryos have grown to eight cells, the genetic tests are run.

The parents can then choose to have only embryos without cystic fibrosis-causing genes implanted to the womb.

Better performance

The technique - pre-implantation genetic diagnosis (PGD) - has been around for some time, but the diagnostic test used could only identify a mutation responsible for 60% of all cystic fibrosis.

Now researchers in Holland have fine-tuned the test.

Mr Jos Dressen, from the Academic Hospital in Maastricht, said: "It means the cystic fibrosis status of more than 90% of embryos will be able to be determined."

He said the test was 99.5% reliable.

"It is distressing enough for a couple to know that they have a one in four chance of a baby having cystic fibrosis.

"It is doubly distressing if pre-natal tests for those whom no PGD was available show the child is affected - then they have to opt to have a disabled child or an abortion.

"Our new technique means we can now offer most couples a way to avoid such a painful decision."

Genetic game of chance

The disease is caused by a genetic abnormality that affects the way chloride ions are transported across cell membranes.

This combines with an increase in sodium absorption to cause excessive mucus secretion in the lungs and digestive tract, increasing the risk of infections.

It affects approximately one child in every 2,500 born, or one a day, the trust says.

However, one person in 25 carries the gene for the disease but will not have any symptoms.

Each time two carriers conceive, there is 25% chance the child will have cystic fibrosis, a 50% chance the child will be a symptomless carrier of the gene and a 25% chance they will be unaffected.

The PGD technique removes most of the chance element and means that only the unaffected embryos are will grow into children.

'More couples will benefit'

Dr Martin Scott of the Cystic Fibrosis Trust said about 30 children had been born as a result of PGD in the UK, but the advance would make the procedure effective for many more couples.

"For people who would not consider terminating a baby and might be holding back from having a baby because they knew they were at high risk, this would be a route whereby they could have a child without cystic fibrosis," he said.

"It is a useful procedure that could help a lot of high-risk couples, although we appreciate it is not available on the NHS."

However, it was possible that in the future the NHS might offer the procedure, he said.

Dr Dreesen was presenting his work at the European Society of Human Reproduction and Embryology annual conference in France.