Complete oocyte activation failure after ICSI can be overcome by a modified injection technique.

BACKGROUND Complete fertilization failure after ICSI is a rare event, and it may happen repeatedly even in cases of normal sperm parameters and good ovarian response. In these cycles, alternative ICSI techniques may prove useful. METHODS Our modified ICSI (mICSI) is characterized by aspiration close to the opposite membrane (the region of the mitochondria with a high inner mitochondrial membrane potential) which is followed by central deposition of the sperm. The method was applied prospectively to ICSI cycles of patients with a history of complete fertilization failure in previous ICSI cycles. In parallel, mICSI was compared with conventional ICSI in terms of further preimplantation development and treatment outcome. RESULTS In patients with previous ICSI failures using conventional ICSI (no 2Pn zygotes out of 70 oocytes that had been injected) application of mICSI led to adequate fertilization (53.6%) and pregnancy rates (33.3%) (P < 0.001; P < 0.01). In patients without previous failed fertilization, no improvement in the rates of fertilization, blastocyst formation, implantation or clinical pregnancy could be seen. CONCLUSIONS Our data indicate that the present version of ICSI is a reliable alternative to conventional ICSI. However, although it overcomes oocyte-dependent activation failure, routine application does not improve the overall results.