Degeneration and post-icsi embryonic development of human MII oocyte in relation to their maturity and morphological characteristics

Abstract

OBJECTIVE: To determine survival and post-ICSI embryonic development of human MII oocytes in relation to their maturity and morphological characteristics. DESIGN: A retrospective study. MATERIALS AND METHODS: Data from human infertility cases that underwent ICSI during 2009 were analyzed. Denuded oocytes were classified as MII, MI (without 1st PB) and GV oocytes and were cultured separately until ICSI. Just prior to ICSI, MI were re-evaluated for the presence of 1st PB (designated as rescued MI oocytes) and used for ICSI. MII stage having abnormal cytoplasm (dark cytoplasm) or fragile oolemma during ICSI were further separated from apparently normal MII after ICSI. After ICSI, oocytes were in vitro cultured separately until Day 3. Rates of fertilization and survival were evaluated at 16-20 hrs post-ICSI and embryos were further cultured for 72 hrs. Day 3 embryos having non-fragmented, even sized, eight blastomeres were classified as top grade 1. RESULTS: During the study period, 206 cases underwent ICSI and 1381 oocytes were injected. The incidence of degeneration after ICSI in the normal MII (9.0%, P<0.05) was significantly lower than that in the MII having either abnormal cytoplasm (18.6%) or fragile oolemma (28.7%) and rescued MI (18.6%). The rate of top grade 1 in the normal MII was 15.2% that was significantly higher than the rates in the MII with abnormal cytoplasm (9.9%) and the rescued MI (6.2%, P<0.05), but was not different from the rate in the MII with fragile oolemma (14.5%). CONCLUSION: Although the fragile oolemma showed the highest degeneration rate, the rate of oocytes developed to grade 1 was significantly higher compared to the MII with abnormal cytoplasm and the rescued MI. The lowest rate of top grade in the rescued MI indicates that oocyte's maturity is one of the critical factors to determine the subsequent development. Therefore morphological assessment of oocytes may be a good indicator to predict the fertilization and embryo development in ICSI.