Fertilizing ability of sperm with unexplained in vitro fertilization failures as assessed by the zona-free hamster egg penetration assay: its prognostic value for sperm-oolemma interaction

Abstract

To investigate the fertilizing ability of sperm with previous unexplained IVF failure using the zona-free hamster egg penetration assay. Three hundred ninety-six tests were performed after multiple IVF failures. In a subsequent prospective study, 38 IVF attempts using the microdrop insemination technique and 81 subzonal inseminations (SUZI) were performed. One hundred thirty-two tests with donor sperm were carried out as controls. Three hundred fifty-two patients who had a minimum of two unexplained IVF failures including at least 10 metaphase II oocytes were included in the study. The ability of the patient sperm to bind to hamster oocytes was lower than that of controls. The largest differences were the percentage of oocytes with swollen sperm heads and the mean number of decondensed sperm heads per penetrated oocyte: both were much lower for patients than controls. Patients with a test result nil did not fertilize any oocytes during the SUZI cycles (n = 7; 50 oocytes), and the post-SUZI fertilization rate for patients with a test value < 10% was significantly lower than that of others (5.4 +/- 10.3 versus 23.8 +/- 8.4, respectively). The defect of sperm involved in IVF failures is mainly a reduction of their fusiogenic ability and not their ability to recognize and bind to the oolemma. Patients with a test result < 10% had a significantly reduced post-SUZI fertilization rate. A test score of zero indicates a major and permanent impairment of the sperm fusiogenic ability.