How do we define male subfertility and what is the prevalence in the general population?

Several semen parameters are used to discriminate the fertile male from the subfertile male. The most widely used parameters are sperm concentration, motility, progressive motility and sperm morphology. Of these parameters, sperm morphology is the single indicator most widely debated in the literature. A large number of classification systems have been used to describe the factors that constitute a morphologically normal/abnormal spermatozoon. The most widely accepted classification systems for sperm morphology are the World Health Organization (WHO) criteria of 1987 and 19921,2 and the Tygerberg strict criteria, now also used by the WHO since 19993-6.