The relationship between critical evaluation of sperm morphology and the TYB-optimized zona free hamster oocyte sperm penetration assay

The objective of this study was to analyse the relationship between the percentage of spermatozoa in semen with normal morphology, assessed using the Tygerberg criteria, and sperm fertilizing ability assessed using the TYB‐optimized zona free hamster oocyte sperm penetration assay (TYB‐optimized SPA), to evaluate the predictive value of strict morphology on outcome of the SPA. In a retrospective study, 56 samples were analysed. In addition to routine semen parameters, the percentage of spermatozoa with normal morphology (A forms) and the average number of penetrations per oocyte (Sperm Capacitation Index) was evaluated in all cases. Using a multiple linear regression analysis with all semen parameters, sperm morphology was the best predictor (p=0.001) of the SPA score. The agreement between the percentage of A forms and the Sperm Capacitation Index beyond chance (kappa coefficient) was 0.5842. Twenty‐two specimens had abnormal SPA scores, with 21 exhibiting abnormal sperm morphology (Sensitivity=96%). The remaining 34 samples had normal Sperm Capacitation Index values; of these, 23 had normal sperm morphology in semen (Specificity=68%). The positive predictive value was 96%, and the negative predictive value was 66%. All semen samples from control donors had normal semen parameters and Sperm Capacitation Index values. In conclusion, the percentage of spermatozoa with normal morphology assessed using Tygerberg criteria (>14% A forms) are predictive of the results in the TYB‐optimized SPA. However, sperm morphology appears to be a better predictor when it is normal than when it is abnormal.