Fresh vs. frozen, no difference

cold girl

Embryos created from vitrified oocytes are just as likely to produce a successful pregnancy as fresh oocytes. Dr. Ana Cobo, Cryobiology Unit Director at Institut Universitari IVI Valencia, Spain told delegates at the ESHRE annual meeting that this research should make egg donation safer, easier and the desired results more predictable in the future.

The randomized clinical trial involved 600 recipients of both freshly harvested oocytes and those preserved using the “new” vitrification method. Vitrification occurs when water is pulled from the cell avoiding the formation of ice crystals which can damage the oocyte and lead to miscarriage. Women who received the vitrified eggs had successful pregnancy rate of 43.7% compared to the fresh oocyte recipients who experience a success rate of 41.7%.

“Because we were able to show that there were no differences between the two groups before embryo implantation,” said Dr. Cobo, “we can be certain that the on-going pregnancy rates in both groups were not influenced by any factor other than the method of oocyte preservation. Although there ahs been considerable circumstantial evidence that cryopreservation by the vitrification method produces results as good as those with freshly-harvested oocytes, until this trial there was still a lack of large randomly controlled studies in the field.”

When fresh oocytes are used there is a sequence of events which must happen precisely: ovulation of the donor, harvesting of the egg, preparation of the sperm, in vitro fertilization or ICSI, and readiness of the recipient’s uterus. When vitrification is used, this level of coordination is not necessary. The eggs are frozen and banked. Ready to go when the mother is. It may be for this reason that there is a very slight advantage for the vitrified oocyte.

Source: ESHRE, Medical News Today


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