Sperm morphology classification: a rational method for schemes adopted by the world health organization

Sperm morphology is an important measure of testicular health, spermiation, and fertility potential. The World Health Organization (WHO) Semen Manuals advocate different sperm morphology schemes, but, like the schemes themselves, do not describe classification sequence or rules that can be unambiguously applied in a standard method. Our novel dichotomous key provides a rational decision framework for a sperm morphology classification algorithm. Classification order hierarchy is standardized and sperm characteristics are defined. Normal morphology is derived after eliminating abnormal and borderline normal forms. By defining and categorizing borderline normal forms separately from either normal or abnormal, the method can simultaneously produce results for Strict and traditional morphology schemes as adopted by different versions of the WHO Semen Manuals. The algorithm can be used for "recalibration" to a less stringent and potentially more relevant standard of normal, while reducing shift, drift, and variation in classification within and among analysts.