Embryo Morphology and Euploidy Rate: A Cross-Sectional Analysis of Day-3 and Blastocyst-Stage Quality

To evaluate the association between embryo morphology at the cleavage stage (Day 3) and the blastocyst stage and the likelihood of euploidy.

This retrospective cross-sectional study included 519 embryos from 250 patients who underwent controlled ovarian stimulation with either oral progestins or gonadotropin-releasing hormone (GnRH) antagonists, followed by intracytoplasmic sperm injection (ICSI) and preimplantation genetic testing for aneuploidy (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, according to the 2011 Istanbul Consensus). Blastocysts were graded using the Gardner classification and categorized as top quality (≥3BB) or non-top quality. Associations between morphology and ploidy were analyzed using the chi-square test or Fisher's exact test, as appropriate, and expressed as odds ratios (ORs) with 95% confidence intervals (CIs).

Among the 519 embryos, 140 (26.9%) were euploid and 379 (73.1%) were 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 twice the euploidy rate of non-top-quality blastocysts (36.9% vs. 18.7%, p<0.001). No significant association was found between Day-3 cell number and euploidy (p=0.550).

Embryos with ≥8 cells on Day 3 were more likely to develop into top-quality blastocysts and exhibited less fragmentation. Although blastocyst morphology was associated with euploidy, Day-3 parameters alone were not predictive. These findings highlight the importance of combining morphological and genetic assessments for embryo selection.