A Comparison Between the Assisted Reproductive Technology Outcomes of Using Two Media During Sperm Microinjection: A Bicarbonate Medium (One-Step) Vs. a Hepes-Buffered Medium (Synvitro Flush) Publisher



Hosseini A ; Borzouei Z ; Naghshineh E ; Tehrani HG ; Vatanparast M
Source: Clinical and Experimental Reproductive Medicine Published:2026

Abstract

Objective: Hydroxyethyl piperazine ethane sulfonic acid (HEPES)-buffered media have long been employed in assisted reproductive technology (ART) procedures; however, concerns persist regarding the impact of zwitterionic buffers on intrinsic cellular mechanisms. Limited studies have compared ART outcomes using bicarbonate media versus HEPES-buffered media during intracytoplasmic sperm injection (ICSI). This study compared the efficacy of two media used in ICSI: bicarbonate medium (one-step) and HEPES-buffered medium (SynVitro Flush). Methods: This retrospective study analyzed data from 200 ICSI cycles performed in 2023. Metaphase II oocytes were allocated to a bicarbonate medium (SAGE 1-STEP; Origio) or a HEPES-buffered medium (SynVitro Flush) during the ICSI procedure. Outcomes including fertilization rate, embryo quality and development, implantation rate, clinical pregnancy rate, miscarriage rate, and live birth rate were compared between the two groups. Results: The fertilization rate was significantly higher in the one-step medium (89.04%) than in the SynVitro medium (82.30%; p<0.001). The one-step medium also yielded more cleaved embryos and higher-quality blastocysts (class A/B; p<0.05). Consequently, more embryos were frozen in the one-step group (264 vs. 151), and higher embryo utilization rates were observed. Clinical pregnancy and live birth rates were significantly higher in the one-step group (p<0.05). No significant differences were found in chemical pregnancy rates or live birth rates among cycles utilizing frozen embryos (p>0.05). Additionally, there were no differences observed in miscarriage rates or multiple pregnancy rates. Conclusion: The one-step bicarbonate medium improved cycle efficiency during the ICSI procedure compared to the SynVitro Flush medium. This finding underscores the importance of selecting an appropriate medium. © 2026 Korean Society for Reproductive Medicine. All rights reserved.