Effects of cumulus cells removal after 6 h co-incubation of gametes on the outcomes of human IVF

Purpose To investigate the effects of cumulus cells removal after 6 h co-incubation of gametes on the fertilization, polyspermy, multinucleation and clinical pregnancy rates in human IVF. Methods A total of 1,200 IVF-ET cycles undergoing 6 h co-incubation of gametes in 2009 were included in this study. Inclusion criteria were: female age < 38 years, first IVF treatment, with bi-ovary and normal ovarian response, e.g., 4 similar to 20 oocytes could be obtained. A 6 h period of co-incubation was applied in all IVF cycles. According to the history of infertility, cumulus cells were mechanically removed either 6 h post-insemination or 20 h post-insemination. For couples with primary infertility, or unexplained infertility, or mild oligospermia or asthenospermia, the cumulus cells were removed at 6 h of insemination for the polar body observation (6 h group, n = 565). Of these, 80 cycles received early rescue ICSI due to fertilization failure or low fertilization rate at 6 h of insemination. For couples with secondary infertility and normal semen analysis, the cumulus cells were removed at 20 h of insemination as routine (20 h group, n = 635). Of these, three cycles received late rescue ICSI due to fertilization failure at 20 h of insemination. Normal fertilization, polyspermy (a parts per thousand yen3PN), multinucleation and clinical pregnancy rates were compared between the two groups (rescue ICSI cycles were not included in the comparison in both groups). Results Significant difference (P < 0.05) was observed between the groups regarding polyspermy rates (7.48% in 6 h group and 9.22% in 20 h group). No difference was observed between the groups regarding normal fertilization rates (2PN rate) (64.89% in 6 h group and 65.74% in 20 h group). No difference was observed between the groups regarding multinucleation and clinical pregnancy rates (11.01% and 65.15% in 6 h group, 10.75% and 66.93% in 20 h group, respectively). The clinical pregnancy rate was 51.43% in cycles receiving early rescue ICSI, while no clinical pregnancy was obtained in cycles receiving late rescue ICSI. Conclusion The present results indicate that cumulus cells removal at 6 h of insemination is a relatively safe operation, which yielded comparable normal fertilization rate, multinucleation and clinical pregnancy rates compared with 20 h group. This protocol may be beneficial for early obsevation of fertilization failure and make early rescue ICSI possible.