Relationship between semen quality and human sperm penetration of zona-free hamster ova

Spermatozoa from 22 presumably fertile donors and from the male partners of 43 infertile couples were evaluated for their ability to fertilize zona pellucida-free hamster ova. All "fertile" donors gave positive results ion the interspecies in vitro fertilization test; 26% of the male partners (patients) gave negative results. Correlations of in vitro fertilization rates and standard semen analysis results indicate that, except for extremely low semen values, sperm fertilizing capacity in vitro could not be predicted accurately from ejaculate sperm number, motility, or morphology. Sperm motility evaluation agreed better with in vitro fertilization test results than did either sperm number or morphology; however, 9 of 31 patients (29%) with normal sperm motility in the ejaculate were judged subfertile in vitro. Also, although higher in vitro fertilization rates were related to greater numbers of normal parameters in a semen sample, 8 of 25 male patients (32%) appraised as "normal" according to the usual semen analysis yielded below-normal in vitro fertilization results. These results support the idea that deficient sperm fertilizing capacity often is a characteristic of poor-quality semen. However, deficiencies in fertilizing capacity also were observed in patient semen samples with excellent properties. Therefore, the interspecies in vitro fertilization test might be useful as an additional tool in clinical investigations of the fertility of the male partners of childless couples, particularly in cases in which infertility continues for no readily apparent reason.