Pre-implantation genetic diagnosis (PGD) is not something that parents embark on lightly or for trivial reasons. For each potentially risky and emotionally draining procedure undertaken, there is only a one-in-four chance that an unaffected baby will be born. Put more starkly, three out of four attempts will end in failure.

In addition to all the risks for mother and child faced by those having IVF (which is essential to this procedure), from hyperstimulation of the ovaries to multiple birth, there are cruel twists of fate unique to PGD.

For instance, none of the embryos obtained in a cycle may be unaffected, or the only one that is may fail to implant properly, with the pregnancy ending in a miscarriage. Only in families devastated by their genetic inheritance will a couple consider putting themselves through such a desperate experience with such a low chance of success.

In this case, women in three generations of the husband’s family had developed breast cancer in their twenties.

This, then, is a procedure for the few, not for the many. In fact, since PGD first became possible in the early 1990s, only about a hundred couples a year have taken it up.

The only other routes are either to adopt children or for a couple to have amniocentesis in the early months of pregnancy, followed by termination of affected pregnancies.

For many parents this is unacceptable and could easily result, especially if the mother is older and having problems with fertility, in having no children at all.

The ethical issues surrounding PGD are already complex but testing for BRCA1 adds a further dimension. “It’s about susceptibility, not inevitability,” says Professor Peter Braude, who heads Britain’s biggest PGD centre at Guy’s Hospital, South London. “The presence of the BRCA1 gene confers an 80 per cent chance of developing breast cancer but breast cancer is not inevitable.”

A baby girl with the BRCA1 gene might never develop a genetic form of breast cancer. On the other hand, even in those unaffected, the risk of breast cancer is not abolished completely because just being female gives women a one-in- nine lifetime risk of breast cancer. There are a number of other “susceptibility” genes for inherited forms of cancers, including bowel cancers. The risk varies from 50 to 80 per cent, which raises the question: how big does a risk have to be?

There can be no hard and fast answer to this. Instead counsellors look at the impact that a disease has had on a family.

There are other ethical issues that have been the subject of prolonged debate in recent editions of Inside the Ethics Committee concerned with prenatal testing for genetic forms of cancer. The first is that cancer is not necessarily lethal. Breast cancer is increasingly a treatable disease, with four out of five women surviving five years or longer. If this is the case, then some would consider that it should not be the parents who should decide the future of an affected baby.

Instead it should be for the child to decide when an adult whether they want genetic information and what they should do about it.

Vivienne Parry presents Inside the Ethics Committee on Radio 4

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