Bologna, Italy Scientists have for the first time transplanted defrosted human ovarian tissue into a mouse, extracted eggs and made them potentially fertilizable -- an advance that could allow women to delay motherhood or safely restore fertility to women who have their ovaries removed.
Scientists said the technique, which is to be presented today at a four-day conference of the European Society of Human Reproduction and Embryology, would be most effective if women freeze their ovarian tissue in their early 20s, because a women's capacity to produce eggs diminishes with age.
"We have a very good option for men who are having chemotherapy -- we freeze their sperm," said the project's leader, Dr. Ariel Revel, an Israeli doctor who is working at the University of Toronto. "We don't have anything for women. This shows that this could be one of the ways."
Revel's method uses animals to foster ovaries until the eggs are grown large enough to be extracted and stimulated to reach maturity in the lab.
In the past, scientists have grafted tissue into animals and detected small eggs, but this is the first group to obtain mature eggs.
Another method used in experiments last year also has been considered a promising approach to restore fertility. Doctors were able to transplant the ovarian tissue of a 30-year-old woman back into her body to help her overcome the discomforts of premature menopause.
Scientists presented that method mainly as a way for women undergoing cancer treatment to regain their fertility after chemotherapy. But the ovarian tissue of women who have cancer can contain cancer cells. Studies have shown that cancer can be transferred to mice when cancerous ovarian tissue is implanted in their bodies.
"The idea is to find a mechanism to resolve her fertility, using her own eggs, without transferring cancer back into her body," said Dr. John Yovich, director of the Pivet Medical Center in Perth, Australia, who was not connected to the research.
Simply extracting eggs from the body and freezing them has not proven very successful because they are damaged by the process. The approach also may not be practical.
Statistics indicate that while 60 percent of defrosted sperm is viable, there's a less than 1 percent chance that an egg would recover, which means 100 eggs would have to be frozen to achieve one pregnancy, Revel said.