INFERTILE COUPLES WITH NORMAL COUNTS WHO REQUIRE SUBZONAL SPERM INSERTION POSSESS A FERTILITY DEFECT THAT AFFECTS ZONA-PELLUCIDA PENETRATION

The results of subzonal sperm insertion (SUZI) have been retrospective ly analysed in a subset of patients with normal sperm counts who were found to require SUZI because of poor or absent fertilization of zona- intact oocytes. This patient group is of particular interest because m ale factor-related infertility cannot be due to insufficient numbers o f spermatozoa reaching the oocytes. Thus, failed fertilization can be attributed to deficiencies in one or more steps in the fertilization p rocess, and SUZI provides a method of distinguishing defects of zona p ellucida penetration from gamete fusion. A total of 26 such patients w ere treated identically to and concurrently with a much larger group o f SUZI candidates who typically suffered from oligozoospermia, and fer tilization results were compared. Fertilization rates after SUZI were higher in patients with normal counts than in oligozoospermic patients (51 and 26% respectively), indicating that the proportion of spermato zoa capable of fusing with the oocyte is the same or higher in the gro up with normal counts. In addition, nearly all SUZI procedures led to fertilization (23/26), with two out of three failed fertilizations occ urring in cases where two or less oocytes were manipulated, results wh ich further indicate that failed fertilization in these patients is no t due to a defect at the level of gamete fusion. These findings sugges t that infertillty in these patients is based upon the inability of th e spermatozoa to reach the oolemma and thus, that their fertility defe ct resides at the step of zona penetration.