Predicting blastocyst viability: the role of post-vitrification re-expansion speed and its correlation with...

Post-thaw blastocyst behavior is clinically relevant and closely linked to implantation and pregnancy success after frozen embryo transfer. Re-expansion of the blastocyst after warming is recognized as an important indicator of embryo viability and has been associated with clinical outcomes, although it is not routinely evaluated in a dynamic manner. In addition, blastocysts undergo different laboratory procedures before vitrification, such as trophectoderm biopsy for genetic testing and artificial collapse, which may influence post-thaw re-expansion dynamics. Therefore, this study aimed to dynamically assess post-thaw blastocyst re-expansion and to evaluate its association with pregnancy outcomes, as well as to examine differences in re-expansion dynamics across different laboratory procedures.

A total of 463 frozen embryo transfer cycles were analyzed, including 170 cycles selected for detailed morphokinetic evaluation. Blastocysts were categorized according to pre-vitrification procedures into a Control group, a biopsy group, and an artificial collapse group. After thawing, the initial re-expansion ratio (T1) was slightly lower in the artificial collapse group compared with the Control and biopsy groups, although this difference was not statistically significant (p = 0.096). The artificial collapse group demonstrated a significantly higher maximal re-expansion ratio (p = 0.031) and a longer time to reach this maximum (p = 0.015). Re-expansion speed was highest in the artificial collapse group, followed by the biopsy group and the Control group, and showed a strong positive correlation with pregnancy outcomes (p = 0.011). Blastocysts in the highest Average Re-expansion Speed Rate (ARSR) quartile (≥ 5.1%) were more than three times more likely to result in pregnancy compared with those in the lowest quartile. The highest ongoing pregnancy rate was observed in the artificial collapse group (52.6%), followed by the biopsy group (41.7%) and the Control group (35.9%) (p = 0.033).

A dynamic assessment of post-thaw blastocyst re-expansion is strongly associated with pregnancy outcomes after frozen embryo transfer. Differences in re-expansion dynamics were observed between blastocysts subjected to different laboratory procedures, with artificial collapse before vitrification showing the most favorable profile. This approach may provide a useful tool for improving embryo evaluation and supporting clinical decision-making in IVF.