Key elements of a highly efficient intracytoplasmic sperm injection technique: Ca2+ fluxes and oocyte cytoplasmic dislocation

Abstract

Objective: To analyze the mechanism by which modifications of the intracytoplasmic sperm injection (ICSI) technique influence success rates.

Design: Prospective clinical study supplemented with an experimental analysis of Ca2+ fluxes provoked by the injection procedure.

Setting: Private hospital and public research center.

Patients: Patients treated by IVF and ICSI.

Interventions: Intracytoplasmic sperm injection.

Main outcome measures: Fertilization and pregnancy rates and intracellular free Ca2+ concentration.

Results: The inclusion of vigorous aspiration of oocyte cytoplasm improved outcomes of ICSI. In a series of 100 consecutive cases treated with this technique, the fertilization and pregnancy rates were 87% of total metaphase II oocytes injected and 52% of total treatment cycles, respectively. Enhanced Ca2+ influx into the injected oocytes and dislocation of the oocyte cytoplasm, including the development of a focus of persistent Ca2+ discharge around the injected sperm head, were the main characteristics of this highly successful technique.

Conclusions: Vigorous aspiration of oocyte cytoplasm may facilitate fertilization after ICSI by increasing the oocyte Ca2+ load at the time of injection, by establishing a more intimate contact of the injected sperm head with oocyte intracellular Ca2+ stores, or by a conjunction of these mechanisms.