Similar Outcomes Seen With Fresh and Frozen Donor Oocytes

June 20, 2013

By Will Boggs, MD

NEW YORK (Reuters Health) Jun 20 - Outcomes of oocyte donation cycles are similar with fresh and vitrified oocytes, researchers from Spain report.

Oocyte donation usually requires synchronization of the donor and the recipient, but oocyte cryopreservation could avoid this scheduling step by creating oocyte banks that allow the patients and the medical team to choose the best timing for the transfer.

Dr. M. Sole from Institut Universitari Dexeus and Universitat Autonoma de Barcelona and colleagues compared the outcomes with fresh and vitrified oocytes from the same donor but different recipients to determine the possible effects of freezing on the viability of the oocytes and the resulting embryos.

Their report in Human Reproduction, online June 5, included 2,087 oocytes from 99 oocyte donation cycles.

Partly due to the difference in oocytes received and the oocytes lost to the vitrification process, there were significantly more fresh oocytes inseminated (mean, 11.1) than vitrified oocytes inseminated (mean, 8.6) (p<0.01).

Despite this difference, the researchers found no significant differences between the two groups in fertilization rates (80.7% for fresh oocytes, 78.2% for vitrified oocytes), ongoing embryos (71.0% vs. 68.2%, respectively), or good-quality embryos (54.1% vs. 49.8%).

Live birth rates and ongoing pregnancy rates per transfer did not differ between fresh oocytes (38.4% and 39.4%, respectively) and vitrified oocytes (43.4% and 44.4%), and there were no significant differences between the groups in transferred embryos, clinical pregnancy rates per transfer, implantation rates, miscarriage rates, or multiple pregnancy rates.

Results were similar for clinical outcomes after transfer of frozen embryos derived from fresh oocytes and vitrified oocytes.

"Our results correlate with the comparative studies performed in recipients of oocytes from different cohorts in which no differences were found in terms of clinical pregnancy or implantation rates when comparing vitrified and fresh oocytes," the researchers note.

"These results encourage the use of this technique for other applications, such as fertility preservation, the accumulation of oocytes from successive stimulations for a preimplantation genetic diagnosis or low responders and in patients at risk of ovarian hyperstimulation syndrome," they conclude.

"The problem with the usual approach to vitrification of oocytes is there is routinely a 15 per cent loss of oocytes," Dr. Sherman Silber from Infertility Center of St. Louis in Missouri told Reuters Health by email. "People writing scientific papers on this subject usually do not mention this or just gloss over it,�but you can hardly say that frozen is the same as fresh if there is a 15 per cent loss, which almost everyone experiences."

"With the same technique using embryos, there is virtually no loss," Dr. Silber said. "So these results are not reassuring for infertility patients who need to freeze their eggs. It is only verification that it is feasible, but not necessarily advisable to use frozen oocytes for a donor egg bank. There will be losses for sure, but with young fertile donors, it may not affect pregnancy rate. Or it may in some special cases where the donor was not that good, and fresh oocytes might have given better results in some of those cases."

"If done correctly, and not everyone does it correctly, there should be no difference in results between fresh and frozen embryos at any age," Dr. Silber added. "So we very freely freeze (vitrification) embryos of infertility patients, so that we can do the transfer later in a more receptive endometrium. The results therefore if anything are better in many cases using frozen embryos. But I repeat, this is only for the few clinics that do it well."

Dr. Sole did not respond to a request for comments.


Hum Reprod 2013.


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