In PGD, a cell is taken from an eight-cell embryo for testing
A woman from London will give birth next week to the first British baby screened to be free of an altered gene which causes breast cancer.
Women in three generations of her husband's family have been diagnosed with the disease in their 20s.
A girl born with the altered gene would have a 50-80% chance of breast cancer - but screening can prevent this.
But one expert warned the technique would not be suitable for all couples with this disease in their family.
Pre-implantation genetic diagnosis (PGD) involves taking a cell from an embryo at the eight-cell stage of development, when it is around three-days old, and testing it.
Using PGD to ensure a baby does not carry an altered gene which would guarantee a baby would inherit a disease such as cystic fibrosis, is well-established.
But in 2006, the Human Fertilisation and Embryology Authority said doctors could test for so-called susceptibility genes, such as BRCA1.
Everybody carries a version of these genes - in fact a properly functioning BRCA1 protein helps stop cancer before it starts - but some particular variations of the genes greatly increase the risk of cancer.
Carrying the key BRCA1 mutation in this family's case would have given up to an 80% chance of developing breast cancer later in life.
BRCA1 and a related version of another gene, BRCA2, account for around 5% of breast cancers.
Many women who discover they have inherited one of the gene mutations choose to have a double mastectomy to remove their breasts.
'A new era'
In this case, the 27-year-old woman and her husband, who are being treated by fertility expert Paul Serhal at University College Hospital London, do not yet know if they are having a girl or a boy.
The couple, who wish to remain anonymous, want to eradicate the gene flaw from their family. The husband's grandmother, mother, sister and a cousin have been diagnosed with the disease.
While a daughter could have been affected by breast cancer herself if she carried the altered gene, a son could have been a carrier and passed it on to any daughters.
Mr Serhal said: "The whole objective of this exercise is not just to make sure the child doesn't have the gene, but to stop the transmission from generation to generation."
He said it was "an exciting new era," adding that it would be possible to screen for any mutated gene which had been linked to a specific cancer.
But he said that, in this case, not carrying an altered BRCA1 gene would not guarantee any daughter born to the couple would be unaffected by breast cancer because there are other genetic and environmental causes.
Dr Alan Thornhill, scientific director of the London Bridge Fertility, Gynaecology and Genetics Centre, said: "While the technology and approach used in this case is fairly routine, it is the first time in the UK that a family has successfully eliminated a mutant breast cancer gene for their child.
"It is a victory for both the parents and the HFEA that licensed this treatment.
'Not a cure'
But Professor Peter Braude, director of the Centre for PGD at Guy's Hospital in London, said: "The decision as to whether PGD is appropriate for a couple will be made after a thorough discussion with knowledgeable genetic counsellors and clinical geneticists.
"It will not be suitable for everyone who has experience of breast cancer in their family, nor where the chances of the IVF needed for PGD has a low chance of succeeding."
Dr Lesley Walker, of Cancer Research UK, said: "This is an exciting step forward in preventing this inherited form of breast cancer but very few people have sufficiently high risk genes to warrant this sort of intervention."
Josephine Quintavalle, of the campaign group Comment on Reproductive Ethics said: "The most important thing is that people realise this is not a cure for breast cancer.
"In addition, we must not forget the embryos which were discarded because they did carry the gene.
"Moving to screening embryos for susceptibility genes, rather than inherited conditions, has broken through a barrier.
"What next? It is going further along the line which ultimately ends in designer babies."