Sperm morphology and IVF pregnancy rate: comparison between Percoll gradient centrifugation and swim-up procedures

Many groups currently use two methods for the separation of motile spermatozoa, swim-up (S-up) and centrifugation on discontinuous Percoll gradient (PGC), and comparison of results indicates that PGC is superior. In this study we have attempted to identify the factors explaining this difference. This laboratory has long-standing expertise in seminology, thus the parameters of sperm morphology were the obvious first choice for detailed study. First, the respective effects of S-up and PGC on sperm morphology were analysed in different types of ejaculates: 62 semen samples with normal parameters and 41 with poor parameters. Both separation techniques resulted in improved morphology in the final preparation but only the increase of morphologically normal spermatozoa in the final Percoll suspension was significant. Second, application of these techniques in our in-vitro fertilization (IVF) programme revealed that, together with the improvement of sperm morphology, a higher pregnancy rate was obtained after PGC. The ongoing pregnancy rates per oocyte retrieval were 21.1% for the S-up technique and 33.3% for the PGC technique. These data show that spermatozoa selected by PGC present an improved morphology which we believe to be linked to improvement of the quality of the in-vitro fertilized embryos and ultimately the percentage of successful IVF results.