Advantages of strict (Tygerberg) criteria for evaluation of sperm morphology.

The purpose of this paper was to compare the validity of strict criteria for sperm morphology evaluation with other evaluation criteria in the diagnosis and prognosis of male fertility potential. Adoption of strict criteria is a holistic approach to sperm morphology evaluation which uses optimal preparation and evaluation procedures and criteria for a morphologically normal spermatozoan based on biological evidence. If liberal evaluation criteria are used, two sperm populations will be included in the normal population, namely those that are truly normal and an abnormal population. It was therefore postulated that results of strict criteria evaluation should provide better correlations with functional tests and fertilization outcome. In most studies where strict criteria was compared to WHO criteria it was found that strict criteria was a better prognosticator of expected in-vitro fertilization rates than WHO criteria. With regard to between- and within-observer correlation coefficients and coefficients of variation for repeated evaluations, results obtained using strict criteria compared favourably with or were better than results reported in the literature. Normal morphology, as evaluated by strict criteria, was also highly predictive of the outcome of certain functional tests, such as the hemizona assay and acrosin activity. From these and other data presented in this paper it can be concluded that sperm morphology evaluated according to strict criteria has definitive advantages over the other (liberal) criteria evaluation methods in the prediction of expected in-vivo and especially in-vitro fertilization rates.