The first test-tube baby created from an egg matured in the laboratory and then frozen has been born in Canada.
The baby is doing well, and another three women are pregnant by the same method, researchers told a medical meeting in Lyon, France, today.
The breakthrough offers hope to women with cancer and others unsuited to normal in vitro fertilisation (IVF) treatment.
Conventional in vitro fertilisation (IVF) involves using high doses of expensive hormone drugs to stimulate the ovaries to produce multiple mature eggs.
Hananel Holzer of the McGill Reproductive Center in Montreal
But some women seeking to preserve their child-bearing capacity may not have enough time to undergo ovarian stimulation or may have a condition that makes it dangerous, such as hormone-sensitive breast cancer.
Until now, scientists have never frozen, thawed and then fertilised a lab-matured egg. This multi-step process increases significantly the flexibility of fertility treatment.
The research is still at an early stage and has not yet been proven in cancer patients, Hananel Holzer of the McGill Reproductive Center in Montreal told the annual meeting of the European Society of Human Reproduction and Embryology.
But Dr Holzer and other experts believe it has the potential to become one of the main options for fertility preservation.
Women diagnosed with cancer are likely to be the main beneficiaries, since cancer treatment can make them sterile and they often have no time to take fertility drugs.
At present, there is the experimental option of having ovarian tissue removed, frozen and transplanted back later. But this brings with it a theoretical risk of re-introducing cancer.