Defective oocytes: a new subgroup of unexplained infertility.

OBJECTIVE: To define a new category of unexplained infertility and its potential treatment. DESIGN: Normal infertile couples underwent prospectively, cross-fertilization attempts in which the wife's oocytes were inseminated by the husband and donor semen. After recurrent failure of fertilization, cross insemination of donor oocytes was attempted with the husband sperm. SETTING: In vitro fertilization unit at a teaching hospital. PATIENTS: Three couples who were diagnosed as suffering of unexplained infertility and treated by in vitro fertilization (IVF). RESULTS: The female partner of these couples produced morphologically normal oocytes that were demonstrated to be functionally defective and failed to fertilize in vitro with both husband and donor sperm. Donated oocytes inseminated by the husband's sperm were fertilized in all patients, demonstrating the normal fertilizing ability of the husbands' semen. One patient conceived and delivered after an oocyte donation. CONCLUSIONS: Conclusive diagnosis of defective oocytes as a cause of infertility may be made only after IVF and oocyte donation.