Does Injection of Immature Oocytes During ICSI Increase the Number of Embryos for Transfer?

Abstract

To evaluate the benefit of injecting immature oocytes during ICSI cycles. Retrospective study. This study evaluated 287 ICSI cycles from 2002-2003 inclusively. After retrieval and culture in 5% CO2 for 4-6 hours, all oocytes were stripped of cumulus cells and both meiosis II (MII) mature oocytes and meiosis I (MI) immature oocytes were injected with partner sperm. After confirmation of normal 2-pronuclei fertilization day 1 post-insemination, zygotes were cultured for 3 days before either transfer to the uterus, discard or culture in sequential media for blastocyst formation. Priority was given to embryos derived from MII oocytes at time of transfer. Statistical analysis was performed using SPSS and p value <0.05 was considered statistically significant. ANOVA and Student-Newman-Keuls tests were used to determine independent associations between injection of MI oocytes and outcome parameters (fertilization rate, embryo cleavage rate, number of embryos cryopreserved and number of embryos forming blastocyst). A total of 168 MI oocytes from 190 cycles were included in this study. Twenty-five percent of MI oocytes fertilized normally and 9.3% divided to the 8-cell stage. Only 1.4% of all ICSI cycles involved transfer of an embryo derived from an MI-oocyte and these cycles had significantly fewer (p < 0.05) MII-derived embryos (mean 4.00 +/− 3.16 SD) than cycles where only MII-derived embryos were transferred (mean 9.75 +/− 5.56 SD). The number of MI oocytes retrieved and injected did not impact MII oocyte fertilization, embryo development to the 8-cell stage on day 3 or number of embryos cryopreserved. The number of blastocysts formed from MII oocytes was significantly higher (Mean +/− SD) in ICSI cycles where no MI oocytes were retrieved (5.7 +/− 3.16) compared to cycles when any MI oocytes were present (3.04 +/− 2.33) with a level of significance of p < 0.05. It can be concluded that oocyte fertilization and embryo development is highly compromised after ICSI of immature oocytes, and is unlikely to maximize the number of embryos available for transfer to the patient. Studies are ongoing to evaluate the effect of chemical activation of MI oocytes post-injection on embryo development.