British couples are to be offered a groundbreaking genetic test that would virtually eliminate their chances of having a baby with one of more than 100 inherited diseases.

The simple saliva test, which identifies whether prospective parents carry genetic mutations that could cause life-threatening disorders such as cystic fibrosis, spinal muscular atrophy or sickle-cell anaemia in their children, is to be launched within weeks in Britain, The Times has learnt.

If the procedure, which will cost about £400 per person or £700 for a couple, is widely adopted, it could dramatically reduce the incidence of 109 serious inherited conditions that collectively affect one in every 280 births.

However, the test, which is being launched by the Bridge fertility clinic in Central London, is ethically controversial. Critics argue that the diseases it detects are too rare for most people to need screening, and that it will cause needless alarm. It is also likely to raise demand for embryo screening and abortion.

There are further concerns about medical supervision. While the Bridge clinic will offer it only in conjunction with genetic counselling, Counsyl, the American company that developed the test, also plans to sell it directly to British customers over the internet, for home use without medical advice.

The Counsyl test shows whether people are carriers of mutant genes that cause 109 recessive genetic disorders. People who have a single copy of one of these genes are not usually affected themselves, but if their partner is also a carrier their children have a one in four chance of inheriting two copies and developing the disease.

If the results show that both prospective parents are carriers of a condition, they could choose to have IVF and screen their embryos, so that only healthy ones are implanted in the womb. Other options include genetic testing during pregnancy, with a view to having an abortion if the foetus is affected, sperm donation or adoption.

People with a family history of several of these disorders, such as cystic fibrosis, can already have screening on the NHS. Targeted programmes are also offered to certain ethnic groups, such as people of African and Caribbean descent who have a higher risk of sickle-cell anaemia.

The Counsyl test is a new departure because it screens for multiple conditions simultaneously and is marketed for the general population rather than high-risk groups. It is already offered by several fertility clinics in America.

The company said that, while each disease screened for is individually rare, one in three people will be a carrier of at least one. About one in 165 of the couples it has tested in the US are both carriers of the same mutation, though this may reflect the test’s appeal to people at high risk.

Balaji Srinivasan, Counsyl’s chief technology officer, said the test was inspired by screening in the Jewish community, which has virtually wiped out a fatal recessive disorder called Tay-Sachs disease by discouraging marriages between carriers. “It is something that should be on the radar of every adult before having a child,” Mr Srinivasan said. “Just as you know not to drink alcohol or smoke while pregnant, you should know you can screen against genetic disease. Couples have a fundamental right to know their carrier status and to make reproductive decisions on the basis of that status without outside interference.”

Alan Thornhill, scientific director of the Bridge, said: “These diseases are quite rare, but pretty horrible. This is something that couples can do to reduce their risk at a reasonable cost. We are offering it with counselling, so that couples are properly informed and understand the options if the results are positive.”

However Frances Flinter, consultant clinical geneticist at Guy’s and St Thomas’ Hospital, and a member of the Government’s Human Genetics Commission, said the test has an uncomfortable “eugenic flavour”.

“It plays unnecessarily on people’s fears,” she said.

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