More than 90% fertilization rates after intracytoplasmic sperm injection and artificial induction of oocyte activation with calcium ionophore.

OBJECTIVE

To examine whether fertilization rates after intracytoplasmic sperm injection can be increased by artificial oocyte activation.

DESIGN

Oocytes that failed to fertilize spontaneously by 24 hours after intracytoplasmic sperm injection were treated either with calcium ionophore to induce activation or with solvent only to serve as control. The ability of ionophore-treated and control oocytes to achieve delayed fertilization was compared.

SETTING

Private hospital and public research center.

PATIENTS

Infertile couples treated by intracytoplasmic sperm injection.

INTERVENTIONS

Intracytoplasmic sperm injection.

MAIN OUTCOME MEASURES

Fertilization and cleavage rates.

RESULTS

The mean rate of spontaneous fertilization after intracytoplasmic sperm injection was 32%, but 88% of the oocytes that failed to fertilize spontaneously did so after subsequent exposure to calcium ionophore. Most of these oocytes underwent at least one apparently normal cleavage division. In contrast, delayed fertilization of oocytes not treated with ionophore was an exceptional finding. If only oocytes remaining intact after intracytoplasmic sperm injection are taken into account, the mean global fertilization rate of ionophore-enhanced intracytoplasmic sperm injection was 91%.

CONCLUSIONS

These results show that the failure of oocyte activation is the main cause of fertilization failure after intracytoplasmic sperm injection. If an appropriate, clinically applicable treatment is found to overcome this problem, intracytoplasmic sperm injection can be expected to yield fertilization rates far exceeding those of standard IVF with normal spermatozoa.