A RETROSPECTIVE ANALYSIS OF UNFERTILIZED AND PRESUMED PARTHENOGENETICALLY ACTIVATED HUMAN OOCYTES DEMONSTRATES A HIGH-FREQUENCY OF SPERM PENETRATION

A total of 518 normal-appearing, meiotically mature human oocytes that were judged unfertilized after insemination in vitro were examined fo r sperm penetration by conventional fluorescence and laser scanning co nfocal microscopy with DNA-specific probes. A similar analysis was per formed on 29 single pronuclear oocytes that were presumed to originate by spontaneous (parthenogenetic) activation. The results demonstrate that 22% of the unfertilized oocytes and 52% of the presumed parthenog enetic oocytes were actually penetrated. Sperm penetration occurred in both normozoospermic and male factor cases. The findings indicate the importance of penetration analysis in determining the causes of ferti lization failure that may reside with the male or female gamete, espec ially when assessing the utility of and necessity for assisted fertili zation in subsequent attempts. The results also suggest that the cytop lasmic capacity to decondense sperm DNA may decline more rapidly than the ability of the oocyte to be penetrated and to mount an effective b lock to polyspermy.