Acrosomal morphology as a novel criterion for male fertility diagnosis: Relation with acrosin activity, morphology (strict criteria), and fertilization in vitro

Objective: To determine the relationships between sperm acrosin activity, sperm morphology evaluated according to strict criteria, visually observed acrosomal morphology, and IVF rates. Design: Prospective analytic study. Acrosin activity was determined on all semen samples together with a standard semen analysis. Emphasis was placed on sperm morphology and especially a novel criterion viz acrosome morphology (acrosome index) as recorded with bright field microscopy. Setting: University-based tertiary care center. Patients: Thirty-three couples undergoing IVF or GIFT with two or more metaphase II ova inseminated in vitro. Main Outcome Measure: In vitro fertilization rates of inseminated ova. Results: Strong correlations were found between acrosome index, normal sperm morphology, and IVF rates. An acrosome index cutoff value could be established at >10% normal acrosomes for IVF rates of greater than or equal to 50% (sensitivity and specificity = 100%) and an acrosin activity cutoff value at >18 mu IU/10(6) sperm. A multiple linear regression analysis showed that the acrosome index and acrosin activity added a significant contribution to the explanation of the variation in the fertilization rates. Conclusions: A strong positive correlation was found between acrosome index and IVF rates. Although the numbers of the study are small, the results indicate that the acrosome index possibly may be regarded as an additional tool in the prediction of IVF outcome and especially may be of value in the group of men with severe teratozoospermia, i.e., less than or equal to 4% morphologically normal spermatozoa.