Comparison outcome: fresh and vitrified donor oocytes in egg-sharing

by Krinos M. Trokoudes, M.D., Constantinos Pavlides, M.S., and Xiao Zhang, M.D., Ph.D.
Pedieos IVF Center, Nicosia, Cyprus; and b Cork Fertility Centre, Cork, Ireland

An increasing number of women in developed countries are not having offspring in the early stages of their reproductive life for various social and medical reasons. However, women of more advanced age suffer from impaired fertility related to their decreasing ovarian reserve. A consequence has been a stronger demand for oocyte donation, but a shortage of oocyte donors has accompanied it. The shortage of oocyte donors in most countries in the world has become a major problem for both recipients and fertility specialists. In the western world, for various religious, ethical, regulatory, financial, and other reasons, oocyte donation is not widely available. As a result, cross-border reproductive care has emerged, whereby couples or individuals travel to other countries to receive treatment, they cannot get at home. Fresh oocyte donation is a proven in vitro fertilization (IVF) technology, but it is still restricted by several difficulties, such as donor availability, cost, the need to synchronize donor and recipient schedules, travel requirements, and the inability to quarantine oocytes. Oocyte cryopreservation could be a promising solution for fertility preservation and donor oocyte banking.

Vitrification, a new method of cryopreservation, has been reported to be a simple, cost-effective, efficient method for cryopreservation of mammalian and human oocytes as well as embryos at the cleavage, morula, and blastocyst stage. Vitrification is achieved by combining a high concentration of cryoprotectants with high cooling and warming rates. In theory, crystal formation, which is considered the main cause of cryopreservation injury, can be completely avoided using vitrification.

Although there is a growing body of evidence supporting oocyte vitrification, prospective and well-controlled studies are still needed to investigate the efficiency, reliability, and safety of oocyte vitrification in donation programs and for future banking. In the clinical practice of oocyte donation, all oocytes have a relatively uniform quality because they are obtained from a young, homogeneous population of donors. In addition, cohort oocytes may be shared among recipients, resulting in a well-controlled model for studying the influence of vitrification on oocyte potential.

In this study, the Cryotop method for vitrification was used in the oocyte-sharing program. The fertilization, cleavage, embryo quality, and clinical outcome of both the vitrified and fresh cohort counter parts were evaluated. This paired study critically assessed the reliability of the Cryotop method and elucidated the potential of this methodology in oocyte banking.

Objective: To compare the survival, fertilization, early embryonic development, and clinical outcomes from fresh and vitrified cohort oocytes.
Design: Review of egg-sharing program, in which the eggs from one donor were shared by recipients of fresh and vitrified eggs.
Setting: IVF center.
Patient(s): 77 women, comprising 36 patients receiving vitrified donor oocytes and 41 patients receiving fresh donor oocytes.
Intervention(s): Shared donor eggs vitrified by the Cryotop method warmed after vitrification, with microinjection of surviving metaphase 2 (MII) or fresh oocytes.
Main Outcome Measure(s): Survival, fertilization, cleavage rate, pregnancy rate, and implantation.
Result(s): Of the vitrified oocytes, 192 (91.4%) survived. There was no statistically significant difference in fertilization and cleavage rates, embryo quality, or clinical results obtained from vitrified compared with fresh oocytes. The outcomes of cycles using fresh oocytes were predictive of the cycle outcomes after warming of oocytes from the same cohort.
Conclusion(s): Oocyte donations using vitrified oocytes can provide the same quality of embryos, pregnancy, and implantation potential as fresh oocyte donations. (Fertil Steril 2011;95:1996–2000. 2011 by American Society
for Reproductive Medicine.)
Key Words: Cryopreservation, IVF, oocyte donation, oocyte vitrification

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