Prediction of fertilization in vitro with human gametes: Is there a litmus test?

OBJECTIVES: The objectives of this study were as follows: (1) to evaluate the relationships between sperm concentration, morphologic pattern, motion parameters, and sperm-zona pellucida binding capacity and (2) to assess their ability to predict fertilization outcome under in vitro fertilization conditions. STUDY. DESIGN: Semen samples from 44 infertile men were prospectively evaluated for density, morphologic pattern (strict criteria), computerized motion parameters (motility, velocity, and linearity), and hemizona assay (outcome expressed as hemizona assay index), and results were correlated with fertilization outcomes of preovulatory oocytes during in vitro fertilization. RESULTS: Of all sperm parameters, morphologic pattern was the best predictor of the ability of the sperm to bind to the zone pellucida. Hemizona assay index was the best predictor of fertilization rate. Stepwise regression analysis provided a model of hemizona assay index plus motility with highest predictability (R² = 53.4%). CONCLUSIONS: (1) The influence of sperm morphologic pattern as a prognosticator of fertilization outcome is established in major part as a determinant of sperm binding ability to the zone pellucida; (2) the hemizona assay provides a robust index that is highly predictive of the potential of human gametes to achieve fertilization and highlights its use in infertility and contraception testing.