Discrepancy between sperm acrosin activity and sperm morphology: significance for fertilization in vitro

Background: In routine semen analysis, discrepancies may occur between sperm acrosin activity test results and sperm acrosomal morphology. Methods: Discrepant test results of sperm acrosin activity (spectrophotometric assay) vs. sperm morphology (strict criteria) in the initial diagnostic investigation of 107 infertile couples were evaluated with respect to fertilization rate (% oocytes with 2 pronuclei) further obtained in IVF treatment. Results: Acrosin activity positively correlated with sperm morphology (% normal forms) (r=0.537) and fertilization rate (r=0.526). ROC curves for the prediction of greater than or equal to50% fertilization rate were comparable for acrosin activity and sperm morphology, with optimal cutoff values at 25 muIU/10(6) sperm and 10%, respectively. In multiple regression analysis, sperm acrosin activity (P=0.002) predicted fertilization rate independently of sperm morphology (P<0.001) and sperm vitality (eosinnigrosin stain) (P=0.03). Acrosin activities greater than or equal to25 muIU/10(6) sperm were observed in 36% of severe teratozoospermic samples (less than or equal to4% normal spermatozoa) associated with low fertilization rate. Twenty percent of the morphologically normal ejaculates showed a low acrosin activity (<25 muIU/10(6) sperm) and low hypoosmotic swelling test (HOST) scores (31.4 +/- 7.6%) and were associated with low fertilization rate. Conclusion: The sperm acrosin assay can help to predict sperm fertilizing capacity in IVF independently of sperm morphology. (C) 2004 Elsevier B.V. All rights reserved.