Strict criteria for the evaluation of human sperm morphology and its impact on assisted reproduction.

Sperm morphology abnormalities can be identified in a large proportion of patients with failed and delayed fertilization when assessing this parameter with strict criteria. Statistical analyses of a large IVF population confirm that, in patients with severe teratozoospermia, fertilization rates can be enhanced in many cases by increasing insemination concentration. However, implantation rates are impaired, thereby affecting the ability of these patients to establish a viable pregnancy. Data from couples undergoing controlled ovarian stimulation/intrauterine insemination seem to support the use of strict morphology as a predictor of outcome in this setting, too. Although a descriptive parameter, sperm morphology assessed by strict criteria can be used as a biomarker of sperm dysfunction(s). These dysfunctions are multiple and include abnormalities of motion parameters, poorer capacity to bind to homologous zona pellucidae and penetrate zona-free eggs, and low incidence of spontaneous and induced acrosome reaction. At a cellular level, poor morphology is associated with a higher content of creatine kinase and impaired capacity to undergo appropriate changes in intracellular calcium concentration. Whether nuclear/DNA abnormalities are present still remains to be fully determined. A definitively objective evaluation of morphology based on these criteria may allow all centres specializing in assisted reproduction to analyse semen in a homogeneous fashion.