Sperm-zona pellucida binding and penetration were assessed on the oocytes that failed to fertilize from couples with >/=3 oocytes treated by standard in-vitro fertilization (IVF). There were four groups: fertilization rate 0% (n = 369), 1-25% (n = 194), 26-50% (n = 81) and 51-95% (n = 100). Of the couples with zero fertilization rate 70% had

Obese fertile men appear to have reduced testicular function. Whether this is cause or effect, i.e. adiposity impairing spermatogenesis or reduced testicular function promoting fat deposition, remains to be determined.

Sperm binding to human ZP is highly selective for double stranded DNA. Sperm with single stranded or denatured DNA bind less or do not bind at all to the ZP, probably because of defects of motility and, more especially, morphology.

More than 75% of motile sperm from fertile men have no ability to bind to the ZP. This finding has important implications for improvement of semen analysis.