Sperm–zona binding and sperm–oocyte penetration analysed by DNA fluorescence: a test for gamete quality after in-vitro fertilization

Sperm-zona binding, sperm-oocyte penetration and pronucleus formation in oocytes obtained after in-vitro fertilization (IVF) failure were studied by analysing DNA fluorescence. Oocytes were classified according to their maturational status, sperm-zona pellucida binding and sperm-oocyte penetration. Spermatozoa were classified as normal or abnormal according to conventional parameters. Sperm-zona binding and sperm-oocyte penetration into uncleaved oocytes were positively related to fertilization: 6.2% of those oocytes from cohorts where none of the oocytes fertilized had > 10 spermatozoa bound to the zona, and 7.7% of them were penetrated. When at least one oocyte per cohort fertilized, these rates were 37.1 and 41.1% respectively. Sperm-zona binding is related more strongly to sperm-oocyte penetration, even without pronucleus formation, than to the maturational status of the oocyte: 26.9% of the oocytes were penetrated by spermatozoa, of which 20.7% had reached the pronuclear stage. For 25 out of 78 couples with a total IVF failure, whatever the spermiogram, defective sperm-zona binding, sperm-oocyte penetration or pronucleus formation was observed. Sperm-zona binding and penetration were positively related, especially when oocytes came from patients with partial IVF failure. Clinical information concerning the fertilizing capacity of oocytes and spermatozoa after IVF failure can be obtained by the simultaneous analysis of sperm-zona binding and sperm-oocyte penetration, and whether or not the latter results in pronucleus formation.