Prospective randomized comparison of non-cryopreserved and vitrified sibling oocyte function and resulting embryo development

Abstract

Vitrification of donor oocytes and establishment of a “Donor Oocyte Bank” has practical, quarantine/disease-testing, and economic advantages. Study aims were to compare oocyte function and embryo development in a pool of sibling oocytes used both as non-cryopreserved oocytes and following vitrification and warming. Prospective randomized clinical study Couples undergoing ICSI elected to participate in this IRB-approved study. Sibling MII oocytes were randomly used in a fresh cycle (NoCryo) or vitrified (Vit). Oocytes were vitrified with dimethyl sulfoxide/ethylene glycol/sucrose with a Cryotip (Irvine Sci). After warming oocytes were observed for survival, incubated for 4h, and inseminated by ICSI. No/normal/abnormal fertilization and oocyte lysis were assessed. Zygotes were placed in G1 media (VitroLife) for growth and assessed for cleavage and embryo development. Statistical analyses were performed by paired Student's t-test. Sixty-nine patients (age: 34 ± 1; ave ± sem) with an average of 18 MII oocytes participated in this study. Post-warming survival was 83 ± 3%. Following ICSI, no fertilization (14 ± 2% vs 11 ± 2%) or abnormal fertilization (1 ± 0.2% vs 2 ± 0.6%) were not significantly different between NoCryo and Vit, respectively. Normal fertilization was significantly higher in the NoCryo group (82 ± 2%) compared to Vit (76 ± 2%; P<0.05), due to increased incidence of post-ICSI oocyte lysis (4 ± 1% vs 9 ± 2%, respectively; P<0.01). Cleavage rate was similar between groups. Day 3 embryos had significantly more cells (6.4 ± 0.1 vs 6.1 ± 0.1; P<0.05) in NoCryo compared to Vit, respectively. Degree of embryo fragmentation was similar between groups. In an infertile population, vitrification of oocytes resulted in acceptable fertilization and embryo development, yet not equivalent to non-cryopreserved oocytes. Knowledge of these oocyte functional and embryo developmental differences will assist in future planning for efficient donor oocyte cryo-banking.