Development of a predictive model for optimal zona pellucida binding using insemination volume and sperm concentration
Objective: To develop a predictive model under hemizona assay (HZA) conditions for human spermatozoa concentrations and insemination volume for optimum zona pellucida (ZP) binding. Design: Analysis of 20 different insemination volumes for zona binding and sperm morphology under HZA conditions. Setting: Reproductive biology unit, tertiary medical center. Patients: Four proven fertile sperm donors. Main Outcome Measures: 5-, 20-, 50-, 80-, and 100-μL droplets were analyzed with four different concentrations of 0.5 x 106, 1.0 x 106, 2.0 x 106, and 4.0 x 106 cells/mL to determine the number of sperm bound to each hemizona. Fifteen hemizonae were used for each insemination volume or microdroplet. Response surface regression model with volume and concentration as the regressor variables has been used. Results: The response surface of binding for the factors concentration and volume showed nonlinear association. A formula, indicating the optimal sperm insemination volume for maximum sperm binding to the ZP, V(max) = -(b1 + b5c)/2b6c, is described. The transformed data indicated 60 μL containing 4 x 106 sperm/mL to be optimal. Although morphology of zona spermatozoa is superior compared with seminal and postswim-up samples, no difference among the percentage of the normal morphology in different microdroplets could be demonstrated. Conclusion: Optimal volume for the obtained concentration of spermatozoa from a patient can be calculated and therapeutically used for cases of severe oligozoospermic patients by microvolume inseminations in IVF practice.