A new test for the assessment of sperm- zona pellucida penetration: relationship with results of other sperm tests and fertilization in vitro

The spermatozoa of some patients attending for in-vitro fertilization(IVF) fail to penetrate the zona pellucida in vitro. A testhas been devised to identify these cases. It is based on thenumber of spermatozoa penetrating into the zona pellucida, whichwere counted after removing spermatozoa bound to the zona surfaceby vigorous aspiration of each oocyte through a narrow gauge(120 µm) glass pipette. The oocytes were collected from197 patients undergoing IVF treatment with their own gametes;79 with no oocytes fertilized and 118 with some oocytes fertilized.Sperm motility, morphology and DNA normality (acridine orangestain) were also measured. The relationships between sperm testresults and IVF rate were examined by logistic regression. Theproportions of penetrated zonae, normal sperm morphology andnormal DNA were the most significant factors related to IVFrate in the whole group. Also, in patients with 30 spermatozoabound per zona pellucida or with normal sperm morphology 30%,the proportion of penetrated zonae and normal DNA were mostsignificant. Oocytes from 42 patients who had zero fertilizationand low sperm-zona binding (average, 2.2 spermatozoa/zona pellucida)were re-incubated with normal donor spermatozoa: large numbersof spermatozoa bound (average, 88 spermatozoa/zona pellucida)and each zona was penetrated by at least one spermatozoon. Inconclusion, the percentage of zonae penetrated was the variablemost significantly correlated with IVF rate. Penetration ofthe zona was also strongly related to fertilization rates inpatients without defects of sperm morphology and sperm-zonabinding. In patients where all zonae were penetrated, poor fertilizationmay be due to sperm morphology and DNA abnormalities. Failureof sperm-zona binding and penetration in vitro in patients withfailure of fertilization was mainly due to sperm defects andnot oocyte defects