Relationships between morphological score changes during embryonic development and pregnancy outcomes

This study investigated whether changes in embryonic morphological scores can predict pregnancy outcomes to support optimal blastocyst selection.

This retrospective dual-center study analyzed 1,492 single blastocyst transfers. Blastocysts were categorized according to day 3 and day 5 scores (excellent, good, or poor) and their day 3-5 morphological changes (improvement, stability, or deterioration). The primary outcomes were clinical pregnancy rate (CPR) and live birth rate (LBR).

No statistically significant differences were observed in CPR or LBR among the Excellent-D3, Good-D3, and Poor-D3 embryo-quality groups. However, both CPR and LBR were significantly higher in the Excellent-D5 group compared with the Poor-D5 group (CPR: 58.64% vs. 46.34%, p=0.014; LBR: 45.97% vs. 33.54%, p=0.012). Temporal trends in developmental outcomes from day 3 to day 5 showed no significant differences across the improvement, stability, and deterioration groups for either CPR (57.95%, 55.28%, and 55.87%; p=0.615) or LBR (43.74%, 44.54%, and 40.84%; p=0.648). In stratified analysis, Poor-D3 embryos that reached Excellent-D5 status had a significantly lower LBR than Excellent-D5 embryos (40.52% vs. 48.81%: odds ratio, 0.714; 95% confidence interval, 0.513 to 0.994; p=0.046). No other subgroup comparisons demonstrated significant differences in clinical outcomes.

Day 5 morphology is the primary predictor of CPR and LBR, with Excellent-D5 embryos demonstrating superior outcomes. Although day 3-5 morphological changes were not associated with CPR or LBR, day 3 quality contributed supplemental predictive value for distinguishing among top-tier day 5 embryos, thereby aiding embryo selection.