Families with a history of genetic disease were given new hope after the birth of the first baby in Britain selected to be free of hereditary breast cancer.
Specialists from University College London spoke of their "absolute delight" after revealing that the girl and her mother were in good health.
The baby grew from an embryo screened to ensure that it did not contain the faulty BRCA1 gene, which passes the risk of breast cancer down generations. Any daughter born with the gene has a 50 to 85 per cent chance of developing breast cancer.
Announcing her birth, Paul Serhal, the medical director of the Assisted Conception Unit at the hospital, said: "They are very well and we are very pleased. This little girl will not face the spectre of developing this genetic form of breast cancer or ovarian cancer in her adult life. The parents will have been spared the risk of inflicting this disease on their daughter. The lasting legacy is the eradication of the transmission of this form of cancer that has blighted these families for generations."
In June, the mother, then 27, told how she decided to undergo the screening process after seeing all her husband's female relatives suffer the disease. The woman, who wanted to remain anonymous, said at the time: "We felt that, if there was a possibility of eliminating this for our children, then that was a route we had to go down."
Cancer charities said the birth raises "complex" issues. Dr Sarah Cant, the policy manager at 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."
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.
Pro-life campaigners condemned the news. James Dowson, of the LifeLeague group, said: "It is not the slippery slope towards designer babies – it is designer babies ... Today it is cancer, next year it will be IQ and the year after that blue eyes and blonde hair."
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.