Amsterdam, The Netherlands: Ultra-fast freezing of ovarian tissue from women who have lost their fertility as a result of cancer treatment can lead to it being used in transplants with the same success rate as fresh tissue, a researcher told the 25th annual conference of the European Society of Human Reproduction and Embryology today (Monday 29 June). Dr. Sherman Silber, Director of the St. Louis Infertility Centre, St. Louis, Missouri, USA, said that freezing tissue by the vitrification method, which avoids ice formation, meant that oocyte (egg) viability was almost identical with that seen in fresh oocytes.
Dr. Silber and colleagues used standard viability testing with fluorescent microscopy to determine the loss or preservation of oocytes in fresh and frozen ovarian tissue of 15 young women undergoing cancer treatment. They also followed up nine homozygotic twin patients after fresh ovary transplantation for the duration of ovarian function and pregnancy outcome, and tested spare tissue that had also been frozen from their ovaries at the time of transplant. Tissue was preserved either by rapid cooling vitrification or by classical slow freezing methods.
"We found that 91.9% of the fresh oocytes were viable compared with 88.9% of those vitrified. However, slow freezing resulted in a 56% loss of viability", said Dr. Silber.
Transplantation of the tissue resulted in a duration of ovarian function of more than four years in five of the seven cases followed up for that long, and all patients regained a normal ovarian cycle within four to five months after the transplant. There was no difference in terms of pregnancy or ovulatory menstrual cycling between fresh and frozen grafts. The scientists used the cortical grafting technique, where very thin slices of tissue are transplanted. This technique is much easier to perform than the delicate microvascular technique, which they described last year in an effort to prevent egg loss and to lengthen the duration of ovarian graft function.
With the microvascular technique, the tiny blood vessels supplying the ovary are directly linked, and ischemia time, during which blood supply is restricted, is minimised. However, this is a very difficult operation not available in most reproductive centres. With the cortical grafting technique, ischemia time for revascularisation was always thought to be a limiting factor, not to mention the deleterious effect of freezing. However, very thin cortical slices not only allow the tissue to be frozen by vitrification, but also accelerate the speed of revascularisation of the ovarian graft.
"We believed that microvascular transplant would give us a longer duration of ovarian function," said Dr. Silber, "but our current research has proved us wrong. This is not only good news for surgeons, but also for patients who will be able to undergo a simpler procedure with equally successful results."
Out of the eight women who received cortical transplants, six have had one or more spontaneous pregnancies, resulting in the birth of seven healthy babies.
"We are in the middle of a massive global infertility epidemic, caused by the new structure of our society where women choose not to have children until they are older," said Dr. Silber. "As a result, many of them become infertile because of the ageing of their eggs and ovaries.
"This procedure is a solution to that social dilemma, allowing women to have children when they are older by preserving their ovaries when they are younger and transplanting them back at a later date. It can also be used to preserve the fertility of young women with cancer who are likely to be cured of their cancer, but who will become sterile as a result of the cancer treatment without such intervention," he said.
European Society for Human Reproduction and Embryology