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