Standard sperm morphology as a predictor of male fertility potential

There are many clinicians who believe that standard sperm morphological criteria as determined by the World Health Organization (WHO) may be one of the most reliable indices of male fertility potential. Many previous studies of sperm morphology have lacked meticulous correction of all female infertility factors in forming their conclusions. Other studies may have compared morphological analysis to either the zona-free hamster oocyte penetration test or fertilization rates with in vitro fertilization/embryo transfer (IVF-ET). The former may not be a valid "gold standard" with which to compare, and the latter might not truly reflect the in vivo situation in view of the markedly different type of sperm-oocyte interaction. These data failed to find a strong correlation of abnormal sperm morphology (as determined by WHO criteria) to identify the subnormal male. When motile densities were normal (greater than 10 x 10(6)/ml), 87% of the female partners of men with normal morphology achieved pregnancies within 6 months compared to 82% with subnormal morphology. Even subnormal motile densities and morphology did not predict the subfertile male. These data strongly suggest that the normals established by WHO for morphology are inadequate to distinguish normal from subnormal. Perhaps increasing the percentage of abnormal sperm morphology to be considered subfertile might prove more useful, or perhaps using another type of morphological assessment might be more effective.