Ultra-Fast Warming Procedure of Vitrified Blastocysts Results in Maintained Embryology and Clinical Outcomes

Vitrification has revolutionized embryo cryopreservation, but represents a significant workload in the IVF lab. We evaluated here an ultrafast blastocyst warming procedure in order to improve workflow while maintaining clinical outcome. We first evaluated the expression of main markers of lineage specification in a subset of blastocysts donated to research warmed with ultrafast protocol. We then performed a prospective pseudo-randomized pilot study comparing blastocyst survival, reexpansion and live birth rates between standard (3 steps, 15 min), and ultrafast warming protocol (1 step, 2 min). Finally, survival, reexpansion and live birth rates (LBR) obtained with ultrafast warming protocol were prospectively collected during 3 months and compared with previous indicators. Immunofluorescence experiments showed that staining and spatial organization of cell fate markers were conserved with ultrafast protocol. Survival, reexpansion and LBR were strictly comparable between standard (n = 47 cycles) and ultrafast (n = 39 cycles) groups in the pilot study (100 vs 100%, 80 vs 76% and 29.8 vs 30.7% in standard and simplified groups respectively). Survival, expansion and LBR obtained with the ultrafast warming protocol over the next 3-month period (321 cycles, 336 embryos) were comparable with those obtained with the standard protocol throughout the 6 months (547 FBT cycles, 578 embryos) preceding shifting protocol (97.6 and 29.6% vs 97.8 and 28.3% respectively, p > 0.05 for both). In conclusion, using an ultrafast blastocyst warming procedure results in similar embryology and clinical outcomes compared with standard protocol, but significantly shortens the technical procedure, ultimately improving the overall lab's workflow.