Microfluidic sperm selection versus density gradient centrifugation in ICSI cycles with abnormal semen parameters: a randomized sibling-oocyte study.

Microfluidic sperm selection (MSS) is a centrifugation-free alternative to density gradient centrifugation (DGC) for sperm preparation in intracytoplasmic sperm injection (ICSI). This prospective, randomized sibling-oocyte study included 55 ICSI cycles from 55 couples treated between February 2025 and February 2026. Eligible couples had abnormal semen parameters according to World Health Organization 2021 criteria. Within each cycle, sibling metaphase II oocytes were randomly allocated to ICSI using sperm prepared by MSS or DGC. The primary outcome was blastocyst formation per two-pronuclear embryo (2PN). Secondary outcomes included fertilization, cleavage, good-quality blastocyst rate, and euploidy rate. Embryo-level outcomes were analyzed using a mixed-effects binomial regression model. MSS was associated with a higher fertilization rate than DGC (82.3% vs. 74.7%; OR 1.60, 95% CI 1.07-2.39; p = 0.022). Cleavage, blastocyst formation (61.8% vs. 65.2%; p = 0.494), and good-quality blastocyst rates were similar between groups. Among 47 cycles undergoing preimplantation genetic testing for aneuploidy, euploidy rates per biopsied blastocyst did not differ significantly between the MSS and DGC groups. Overall, MSS was associated with higher fertilization, while subsequent embryologic outcomes were comparable between groups.