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

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.