A girl due to be born next week will be the first British baby genetically selected to be free of a breast cancer gene.
She grew from an embryo screened to ensure it did not contain the faulty BRCA 1 gene, which passes the risk of breast cancer down generations.
Any daughter born with the gene has a 50 per cent to 85 per cent of developing breast cancer.
In June the 27-year-old mother now waiting to give birth told how she decided to undergo the screening process after seeing all her husband's female relatives suffer the disease.
The woman, who wants to remain anonymous, said: "We felt that, if there was a possibility of eliminating this for our children, then that was a route we had to go down."
The technique, known as pre-implantation genetic diagnosis (PGD) has already been used in the UK to free babies of inherited disorders such as cystic fibrosis and Huntington's disease.
But breast cancer is different because it does not inevitably affect a child from birth and may or may not develop later in life. There is also a chance it can be cured, if caught early enough.
Permission to carry out PGD for breast cancer had to be obtained from the Human Fertilisation and Embryology Authority by the London clinic which performed the procedure.
The body, which licenses IVF clinics and embryo research, gave the go ahead after holding a public consultation.
Doctors at the private clinic housed at University College Hospital conducted tests on 11 embryos by removing just one cell from each when they were three days old. Six embryos were found to carry the defective BRCA 1 gene. Two embryos that were free of the gene were implanted, resulting in a single pregnancy.
Fertility expert Paul Serhal, who led the PGD team, said today: "We have now entered a new era of being able to help people who have cancer genes.
"Not only can we liberate people from the guilt of passing a cancer gene onto their child, we can cut off transmission of the gene once and for all. These are families who have been plagued by this genetic curse for generations. With a wave of a magic wand the job is done, and this is fantastic.
"People who criticise these procedures talk of 'designer babies' but this is nonsense. Clearly you can't prevent what goes on in some remote part of the world, but we can't sit like lame ducks and let this potential misuse stifle the development of science."
Mr Serhal has treated other couples to create babies free from less well known cancer genes. These have included a gene that causes eye cancer, and another that carries a high risk of bowel cancer.
He said the procedure was highly complex and could only be attempted by major IVF centres. But he expected to see PGD screening for cancer genes become more common in the future.
Faulty genes are responsible for between 5 per cent and 10 per cent of the 44,000 cases of breast cancer that occur in the UK each year.
BRCA 1 and its sister gene BRCA 2 are the two most commonly involved. Women with a defective BRCA 1 or BRCA 2 gene are up to seven times more likely to develop breast cancer than those without the mutations.
Professor Peter Braude, director of the Centre for Preimplantation Genetic Diagnosis at Guy's Hospital London said: "I am delighted to hear the news that prevention of yet another serious disorder has been achieved, further demonstrating the important place of PGD as part of the services that should be offered to couples at significant genetic risk.
"Clearly, as the HFEA has recommended after their public consultation, 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 Sarah Cant, policy manager at the charity Breakthrough Breast Cancer, said: "The decision to screen embryos to see whether they have a faulty breast cancer gene is a complex and very personal issue.
"Women with a family history of breast cancer tell us that what might be right for one person may not be right for another.
"It's important for anyone affected to have appropriate information and support so they can make the right choice for them."
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