Effects of abnormal zona pellucida on fertilization and pregnancy in IVF/ICSI-ET

Objective To analyze the fertilization rate, embryo development and clinical outcome of oocytes with abnormal zona pellucida after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Methods A retrospective analysis included a total of 43 cycles (27 IVF cycles and 16 ICSI cycles) in which oocytes displaying abnormal zona pellucida were retrieved between January 2006 and December 2011. The fertilization rate, embryo quality, and the cumulative clinical pregnancy rate were analyzed. Results Rescue ICSI was applied in 27 IVF cycles in which failed extrusion of the second polar body after conventional IVF was observed, and of them, complete failure to fertilize occurred in 23 IVF cycles. The fertilization rate and the normal fertilization rate for IVF (64.83% and 59.32%, respectively) were significantly lower than those for ICSI (85.19% and 79.01%, respectively), whereas the cleavage rate (94.12%) with IVF did not differ significantly from that with ICSI (95.65%, P>0.05). The percentages of good-quality embryos in IVF group (52.67%) and ICSI group (43.75%) also did not differ significantly (P>0.05). Although the rates of implantation and pregnancy appeared to be greater in IVF group (33.33% and 40.00%, respectively) compared with those in ICSI group (25.00% and 35.71%, respectively), the differences were not significant (P>0.05). Conclusions ICSI should be carried out for oocytes with abnormal zona pellucida, for which the risk of IVF failure is high. Rescue ICSI improves the likelihood of fertilization of oocytes with abnormal zona pellucida, but cannot improve the clinical outcome.