An American woman who received ovarian tissue from her sister has become pregnant in what is believed to be the first case of its kind, the conference was told yesterday.
Doctors at St Luke's Hospital in St Louis, Missouri, performed the operation on Melanie Morgan and Stephanie Yarber, twins aged 24.
Stephanie went through the menopause at 13 after developing a rare condition, and was told she would not be able to have children. She and her husband, Kevin, spent $10,000 (£5,500) over six years on unsuccessful fertility treatment.
Melanie, a student nurse who has three children, agreed to donate one of her ovaries to her sister. In a five-hour operation in April, an ovary was removed from Melanie and the outer tissue - which is rich in egg-producing follicles - was implanted into Stephanie's faulty ovaries.
Stephanie is now four weeks pregnant and conceived without the help of any further fertility treatment.
The twins' father, Carlton Fuller, said: "They have always been very close and Melanie wanted to do this for her sister. She has seen her go through so much over the years." Mrs Yarber, who works in public relations and lives in Alabama, said: "It's incredible. I even like the morning sickness."
The twins are identical, and their perfect DNA match meant there was less chance of tissue rejection. But scientists believe the breakthrough may be able to help sisters who are not twins.
An Argentinian team has successfully transplanted ovarian tissue from one sister to another and improved the recipient's fertility, although she is not pregnant.
Richard Kennedy, secretary of the British Fertility Society, sounded a note of caution over the procedure. "It is experimental and I think it is an interesting development but it must still be viewed as an experiment," he said.
"It is only going to be applicable in a small group of people.
"To sacrifice a whole ovary has not-insignificant risks for the woman donating.
"If you donate an ovary and then develop a cyst on the other one and it needs removing, you are going to go through the menopause at a very young age. It is an experimental gamble."