Incomplete denudation of oocytes prior to ICSI enhances embryo quality and blastocyst development

BACKGROUND: Granulosa cells are essential mediators of oocyte maturation and fertilization. Because of the denudation of oocytes in preparation for ICSI, any potential positive effect of surplus cumulus cells (CCs) on further development would be unable to exert further effect. In order to evaluate the actual influence of adhering cumulus cells on further preimplantation development, this prospective study was carried out. METHODS: Sibling cumulus-oocyte complexes for 57 ICSI patients were split into a study group (incomplete denudation, n = 314) and a control group (complete denudation, n = 336). According to the cumulus cell pattern after partial denudation, mature gametes from the study group were further subdivided into type A oocytes, which showed several prominent CC clusters (n = 202), and type B (n = 75), which showed a more homogeneous pattern with CC covering the whole surface of the gamete. RESULTS: In immature oocytes, presence of adhered CCs led to a significant increase in resumption of meiosis (P < 0.01). Fertilization rate (P < 0.05) and ability to cleave (P < 0.01) was impaired in the study group, because of difficulties in ICSI of type B oocytes. By contrast, embryo morphology on days 2 (P < 0.01) and 3 (P < 0.05), as well as blastocyst formation, was better (P < 0.05) in the study group (55 blastocysts out of 88 zygotes) as compared to that in the control group (49/105). CONCLUSION: These data indicate that co-culture of oocytes with attached CCs may enhance preimplantation development.