Shortened warming preserves cellular resilience and accelerates post-warming development in human blastocysts: A...

Conventional multi-step warming protocols (MWP) for vitrified blastocysts are labor-intensive and susceptible to handling variability. This study evaluated whether a shortened warming protocol (SWP) could support post-warming recovery and developmental competence comparable to those of conventional MWP. A retrospective propensity score-matched cohort study was conducted using 546 single vitrified-warmed blastocyst transfer cycles (271 SWP and 275 MWP). Post-warming developmental behavior was assessed using time-lapse imaging, including the start of re-expansion (tSRE), completion of re-expansion (tCRE), and hatching start point (tHSP). Morphological recovery, blastocyst quality score (BQS), and inner cell mass (ICM) and trophectoderm (TE) grades were also evaluated. Blastocysts warmed using SWP demonstrated significantly faster post-warming recovery, with shorter tSRE (0.148 vs. 0.179 h, P = 0.009), tCRE (2.16 vs. 2.91 h, P < 0.001), and tHSP (3.08 vs. 5.24 h, P < 0.001). The SWP group showed a significantly higher proportion of blastocysts with improved post-warming morphology and grade A ICM and TE than the MWP group (P < 0.05). The distribution of hatching stages and clinical pregnancy outcomes did not differ significantly between the groups. These findings suggest that SWP provides efficient and biologically stable post-warming recovery without compromising embryonic quality or clinical outcomes.