Vitrification May Be Viable Option for Oocytes


AMSTERDAM — Vitrified ovarian tissue yields a greater number of viable oocytes after thaw and transplant, compared with tissue that is frozen using conventional techniques, according to data presented at the European Society of Human Reproduction and Embryology.

“Both ischemic loss from cortical transplantation and oocyte loss from freezing can be prevented with ultrathin grafts and vitrification,” said Dr. Sherman Silber, director of the Infertility Center of St. Louis.

In fact, oocyte viability from transplanted vitrified ovarian tissue is similar to that of fresh transplants, he said.

In one study, Dr. Silber compared oocyte viability in 14 young cancer patients who had received ovarian tissue transplants after either vitrification (n = 8) or conventional freezing (n = 6). He compared his results with those of nine patients who had received fresh ovarian tissue transplanted from their identical twins.

Oocyte viability was similar in the twin patients who had received fresh tissue and cancer patients who had received vitrified tissue, but was significantly decreased in cancer patients who had received conventionally frozen tissue, he reported.

“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,” he said.

Ovarian function returned in all patients regardless of whether they had received fresh tissue or tissue frozen by either method, emphasized Dr. Silber. All patients regained a normal ovarian cycle 4-5 months after transplant.

Dr. Silber's data point to the superiority of vitrification over conventional freezing, in terms of oocyte viability. However, another paper presented at the meeting suggests vitrification may result in abnormal expression of a gene known as GAPDH (glyceraldehyde 3-phosphate dehydrogenase). In an in vitro study of human ovarian tissue, “we detected drastically reduced levels of GAPDH-gene expression in ovarian tissue after vitrification, compared with conventional freezing,” reported Vladimir Isachenko, Ph.D., of the University of Ulm (Germany).

“This is a housekeeping gene,” he explained in an interview. “If there is no expression of this gene, or expression is decreased, it will eventually result in cell death,” he said.

Studies to date show no indication of abnormalities in children conceived from vitrified ovarian tissue or oocytes, commented Dr. Silber.

But abnormal gene expression could have very subtle effects that might also not become evident until adulthood, Dr. Isachenko explained. He suggested that the mechanism by which vitrification might alter gene expression might be the direct contact of tissue with liquid nitrogen. Based on his findings, his laboratory no longer uses vitrification.

Oocyte viability from transplanted vitrified ovarian tissue is similar to that of fresh transplants.

Source Dr. Silber

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