EVIDENCE OF SPERM ENTRY INTO ASSUMED UNFERTILIZED HUMAN OOCYTES AFTERSUBZONAL SPERM MICROINJECTION

Sub-zonal sperm microinjection (SUZI) as a treatment for male factor i nfertility can facilitate fertilization, however, in many cases oocyte s remain unfertilized even though the sperm is placed in close contact with the oolemma. In order to improve our understanding of gamete int eraction in cases of failed fertilization, we have analysed the failed fertilized oocytes from both SUZI and conventional in-vitro fertiliza tion. The fluorochrome Hoechst 33342 (which binds specifically to DNA) was used to check for the possible presence of paternal chromatin in the unfertilized oocytes. A significantly higher (P < 0.01) number of microinjected oocytes showed signs of fertilization 2-3 days after spe rm microinjection compared to normally inseminated oocytes, 30/175 (17 .1%) and 2/79 (2.5%) respectively. In addition, four out of eight coup les returning for a second treatment by SUZI displayed anomalies in fe rtilization in both cycles. The semen characteristics of patients with or without anomalies in fertilization was not different. The irregula rities observed in the fertilization process infer that certain male f actor patients have intrinsic sperm anomalies lying at the sperm membr ane and/or chromatin level that could lead to anomalies in the appeara nce of the pronuclei.