Oocyte Vitrification: A Comparative Analysis Between Fresh and Cryopreserved Oocytes in an Oocyte Donation Program

Background: Oocyte Cryopreservation has become an important part of infertility treatment for various reasons such as fertility preservation in women going for oncological treatment; in oocyte donation cycles; in eliminating several religious, ethical, and legal concerns of embryo freezing and in women who wish to delay childbirth. The newer ”vitrification” technique for freezing has further improved the success rates for actual conception than the earlier method of slow freezing. A successful oocyte freezing program can help in establishment of oocyte banks, which would help to provide compatible oocytes immediately, thus would eliminate the several problems of fresh donor cycles. Methods: In this retrospective observational study, total 60 oocyte donation cycles were included (38 were fresh and 22 were vitrified oocytes cycle, respectively). After a thorough screening, controlled ovarian hyperstimulation for donors was performed using flexible antagonist protocol. All mature oocytes were allocated into “vitrified oocytes” and “fresh oocytes” groups. Vitrification technique using Cryotop method was used for oocyte freezing. Both clinical and laboratory outcomes of vitrified and fresh oocytes in donor cycles were compared. Results: A total of 600 oocytes (226 “vitrified oocytes” and 374 fresh oocytes), were studied. After warming 218 oocytes survived resulting in survival rate of 96.4%. Fertilization rate and embryo formation rate was 86.2% and 93.6%, respectively. Results of frozen-thawed oocyte donor cycles were compared with fresh donation cycles. For fresh oocyte group, fertilization rate and embryo formation rate was 83.4% and 92.6%, respectively. On comparing clinical outcomes, clinical pregnancy rate was 60.5% in fresh group and 63.6% in vitrified group. Conclusions: Both clinical and laboratory results obtained in the study suggest that oocyte cryopreservation can be performed with reproducible success, thus vitrification technique can be provided as a useful tool for achieving highly successful outcomes in an oocyte donor program.