Received March 12, 2026
Accepted April 13, 2026

Objective: To evaluate the association between embryo morphology at the cleavage stage (Day 3) and blastocyst stage, and the likelihood of euploidy. Methods: This retrospective cross-sectional study included 519 embryos from 250 patients who underwent controlled ovarian stimulation with either oral progestins or GnRH antagonists, followed by ICSI and PGT-A between 2018 and 2023. Day-3 embryos were classified according to cell number (<8 vs. ≥8) and fragmentation grade (A, B, or C, per the Istanbul Consensus, 2011). Blastocysts were graded using the Gardner classification and categorized as top-quality (≥3BB) or not. Associations between morphology and ploidy were analyzed using chi-square or Fisher’s exact test and expressed as odds ratios (OR) with 95% confidence intervals (CI). Results: Among 519 embryos, 140 (26.9%) were euploid and 379 (73.1%) aneuploid. Embryos with ≥8 cells on Day 3 exhibited significantly less fragmentation (p<0.001) and were more likely to develop into top-quality blastocysts (50.1% vs. 37.7%, p=0.002). Top-quality blastocysts had nearly double the euploidy rate compared to non–top-quality embryos (36.9% vs. 18.7%, p<0.001). No significant association was found between Day-3 cell number and euploidy (p=0.550). Conclusions: Embryos with ≥8 cells on Day 3 were more likely to yield top-quality blastocysts with lower fragmentation. Although blastocyst morphology correlated with euploidy, Day-3 parameters alone were not predictive. These findings highlight the importance of combining morphological and genetic assessments for embryo selection.