Sperm Selection Using Micro Swim-Up: Improvement of Chromatin Integrity Compared to Density Gradient Centrifugation

Abstract

Background: Selecting high-quality spermatozoa with optimal nuclear integrity is a crucial step in assisted reproductive technologies (ART). While density gradient centrifugation (DGC) is widely used, the associated centrifugation steps may induce cell stress, potentially damaging sperm DNA. Conversely, micro swim-up (MSU) is an innovative, centrifugation-free procedure using autonomous gamete migration in a polyvinylpyrrolidone medium. Objectives: This study aimed to compare the sperm selection technique MSU with the conventional method DGC in terms of sperm chromatin integrity in 90 semen samples. Materials and Methods: Rapid progressive motility, sperm DNA fragmentation (sDF; SCD test), nuclear immaturity (aniline blue [AB] staining), and chromatin decondensation (chromomycin A3 [CMA3] staining) were evaluated before and after selection. Results: Both procedures significantly improved motility and nuclear parameters compared to unselected samples. However, MSU outperformed DGC across all nuclear integrity markers. Specifically, sDF decreased from 18.50% (14.63–26.25) to 9.25% (6.00–16.00) with DGC and 1.00% (0.00–2.00) with MSU (p < 0.0001 MSU vs. DGC). Regarding nuclear immaturity, values improved from 21.00% (15.00–27.50) to 15.00% (8.00–18.00) with DGC and 5.00% (4.00–10.00) with MSU (p = 0.012 MSU vs. DGC). Similarly, chromatin decondensation decreased from 18.25% (10.88–23.63) to 13.50% (7.00–15.63) with DGC and 5.50% (2.75–10.00) with MSU (p = 0.0001 MSU vs DGC). Discussion and Conclusion: MSU selects spermatozoa with significantly superior nuclear integrity compared to DGC, markedly reducing DNA fragmentation and improving chromatin maturation. Given the direct impact of these parameters on ART outcomes, MSU might represent a valuable alternative to traditional centrifugation-based methods in clinical settings.