A UK fertility centre is to offer the controversial US genetic test that promises to eliminate the chances of a couple having a baby with over 100 inherited diseases.

The saliva test, developed by US company Counsyl, will be launched by the Bridge fertility centre in central London over the next few weeks. It is already offered at several fertility clinics in the USA. At £700 per couple, the test screens for common mutations in 109 genes, which cause conditions such as cystic fibrosis, muscular dystrophy and sickle cell anaemia. Altogether these diseases affect one in 208 live births.

The test on its own does not prevent the couple having a child with the disease, as many media reports have implied this week. The test simply detects whether the male and female partner carry 'recessive' mutations: as a single copy in the parent they do not necessary have any effect, but if the couple have children there is a one in four chance that the child will inherit both copies of the mutation and have the given disease. In this instance, options for a positive-testing couple include sperm or egg donation. Many also fear that such testing will increase the demand for embryo screening and abortion and lead to 'back door' eugenics.

Although the London Bridge Centre will give genetic counselling as part of its screening service, Counsyl plans to sell the test direct to British customers over the internet.

The NHS already offers targeted screening programs to couples with a family history of some genetic diseases, such as cystic fibrosis, and also to couples with certain ethnic backgrounds, such as African or Caribbean descent who are more prone to carry the sickle cell anaemia mutation. The Counsyl test is novel because it screens for multiple mutations simultaneously and is marketed to the entire population rather than select groups.

Alan Thornhill, scientific director of the Bridge, states: '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'.

Frances Flinter, consultant clinical geneticist at Guy's and St Thomas' Hospital, and a member of the Government's Human Genetics Commission, says the test has an uncomfortable 'eugenic flavour' and that: 'It plays unnecessarily on people's fears'.