Fri 19 Sep 2008
Evidence reflecting the success of human oocyte freezing with the technique of vitrification is now so strong that its use in fertility preservation should be reconsidered, according to a proposal in the journal Fertility and Sterility.
Three senior figures in the field write: “The reported success of the use of this method [vitrification] should stimulate a renewed debate on oocyte storage for fertility preservation without a medical indication.”
The cryopreservation of oocytes has long been a challenge in reproductive medicine, but its success has been elusive and frustrating. Indeed, 2 years ago, at the 2006 annual meeting of ESHRE (European Society of Human Reproduction and Embryology) in Prague, Dr Masa Kuwayama from Tokyo estimated that no more than 150 babies had been born worldwide following oocyte cryopreservation by conventional “slow-freeze” methods.
But the vitrification method he described, which requires the very rapid freezing of cells (to -196oC) in very small volumes of solution, prevents the formation of ice crystals and thereby damage to the oocyte after thawing. Intra-cellular crystallization was believed to be the main cause of damage to the oocyte’s meiotic spindle and chromosome alignment. Vitrification, said Dr Kuwayama, preserves the oocyte in a glass-like state without crystallization, paving the way for a cryopreservation method as effective for female gametes as for male gametes. Results presented in Prague showed that 94.5 percent of 111 cryopreserved oocytes survived thawing, 90.5 percent were fertilized by intracytoplasmic sperm injection (ICSI), and 50% percent of the resulting embryos cleaved sufficiently for transfer. Twelve pregnancies were recorded from 29 transfers, a pregnancy rate of 41.9 percent.
In the short time since that meeting, vitrification has been widely adopted, particularly in countries like Italy and Germany where embryo freezing is banned by law. One recent randomized trial from Valencia found no difference in reproductive potential (survival, fertilization, and cleavage) between fresh and vitrified oocytes in a series of egg donors whose oocytes were randomly assigned to undergo fresh fertilization or fertilization following vitrification and warming an hour later.[2] The authors of this report noted as a result that vitrification of oocytes has “a high potential for establishing oocyte banking.”
Many other studies over recent months have reported similar results, with pregnancy outcomes in vitrified oocytes comparable to those from fresh cycles. Indeed, one group—from Lubeck, Germany—after describing their results for the freezing of zygotes by vitrification, asked: “Is it still fair to advocate slow-rate freezing?”
Such results, however, are in small groups of patients, and rarely in well-controlled trials. Thus, in a recent review of oocyte cryopreservation, one of its research pioneers, Dr Debra Gook from Melbourne, proposed that “the small number of babies born from clinical oocyte cryopreservation and the paucity of well-controlled studies currently preclude valid comparisons between approaches.”[3]
This latest review from three respected figures in IVF suggests that the results now achieved with vitrification are indeed sufficiently robust to at least reconsider fertility preservation as an indication for oocyte freezing.
So far, the indications for oocyte freezing have been only medical—in advance of radio- or chemotherapy, and other conditions of premature menopause. But now, in the face of lower fertility rates and delayed maternal age among women in all developed countries, the authors propose that “the successful preservation of oocytes by vitrification will provide the ‘aging’ woman who has had to delay her childbirth, for any reason, the opportunity to conceive and deliver using her own oocytes at the time she decides.” This is a hot issue in reproductive medicine, and one which, for the first time, may extend treatment from a medical to a social indication.
Orgyn.com
