Doctors have been given permission to screen a woman's embryos for a rare form of eye cancer.
Angela Donovan had retinoblastoma as a child and passed on the gene to her first son, Kieran, who underwent chemotherapy to get rid of the cancer.
Fertility experts at University College Hospital London will test her embryos to prevent any of her future children from contracting the disease.
Critics say screening should only be used for non-curable illnesses.
The move comes just days after the government launched a public consultation about the future of fertility treatment and embryo research.
The licence was awarded by the fertility watchdog, the Human Fertilisation and Embryology Authority.
The authority last week announced a separate consultation on extending the screening of embryos for gene-linked diseases.
Pre-implantation genetic diagnosis (PGD) is currently permitted to check an embryo is free of inherited diseases such as Huntington's disease.
In the process, a cell is removed from an embryo at the eight-cell stage of development, when it is about three days old.
It is then tested for genetic disorders. An unaffected embryo is then selected to be implanted into the mother's womb.
Angela and Louis Donovan are one of the couples who want to use PGD.
Mrs Donovan had the cancer as a child and had her right eye removed when she was four months old.
Kieran underwent cancer treatment
Their son Kieran, now five, inherited the condition from his mother, and had to have chemotherapy, radiotherapy and other treatments to eradicate his cancer.
She says she does not want another child to go through the same experience.
"PGD is the only way for us to be able to have more children," she said.
"Otherwise it's going to be a 50/50 chance that the gene will be passed on.
"It's a big risk to take, and without PGD, we would be left playing Russian roulette - or we wouldn't be having any more children, which would be devastating for me."
Children who inherit the retinoblastoma gene have a 90% risk of developing the cancer.
In most children with retinoblastoma, only one eye will be affected, but in about a third, tumours develop in both eyes.
Experts say nine out of 10 cases can be cured.
Josephine Quintavalle, of the Campaign for Reproductive Ethics (CORE), said she understood no mother would want to see her child suffer.
But she added: "No matter how harrowing cases are, we have to deal with the ethical issues this kind of technique raises on a much broader basis, not one by one."
Dr Paul Serhal, of the Assisted Conception Unit at University College Hospital, will carry out Mrs Donovan's treatment.
He said he hoped embryo-screening would eventually eradicate all gene-linked diseases.