Effect of cumulus cell removal 4 h post-insemination on fertilization and embryo quality: a prospective randomized sibling-oocyte study

PURPOSE: The study was designed to evaluate whether cumulus cell removal 4 h post-insemination could influence fertilization and embryo quality. METHODS: The study included 61couples undergoing standard long down regulation protocol from July 2011 to May 2012. Sibling oocytes of each patient were randomly assigned to either the 4 h group or the 20 group. For the 4 h group, cumulus cells were removed 4 h after gamete coincubation; for the 20 group, cumulus cells removal was performed 20 h after insemination. Fertilization rate, embryo quality, pregnancy rate and implantation rate were assessed. RESULTS: A total of 801 sibling cumulus-oocyte complexes (COCs) were randomized to the 4 h group (421 COCs) or 20 h group (380 COCs). There was no difference in the two pronuclei, one pronucleus and grade 1-2 embryo rate. Three pronuclei rate was significantly higher in the 4 h group compared to the 20 h group (12.6 % vs. 8.2 %, P = 0.041). Comparison of embryo transfer cycles in which either embryos from the 4 h group or 20 h group were transferred did not reveal any statistically significant differences in pregnancy or implantation rates. CONCLUSION: The results of the present study indicate that cumulus cell removal 4 h post-insemination may increase the percentage of tripronuclear zygotes. However, normal fertilization rate, embryo development, clinical pregnancy rate and implantation rates are not influenced by the timing of cumulus cell removal.