[Study of sperm fertilizing ability in male infertility using the zona free hamster egg penetration assay].

Zona free hamster egg-sperm penetration assay (SPA) was performed on 50 normal fertile men and 58 infertile men. The median penetrating rate was 68% (13%-100%) for the fertile men and 11% (0-100%) for the infertile men. These existed no clear relationship between SPA and any other sperm parameters. SPA showed the best diagnostic rate (72.4%) for male infertility, which was evaluated by the 95% specificity threshold values of normal males. Therefore, SPA is best correlated with male impregnating ability. On the contrary, the infertile diagnostic rate of sperm density was relatively low (36.8%). SPA was also carried out on male partners of unexplained infertility couples, and 8 out of 36 (22%) showed decreased sperm penetration rate (less than 10%). In these couples, the deterioration of fertilizing ability was thought to be one of the causative factors of infertility.