Grade 1 Embryo in IVF
A Grade 1 embryo represents the highest quality embryo classification in IVF, characterized by equal-sized blastomeres with no fragmentation, and is associated with the best implantation and pregnancy rates. 1
Morphological Characteristics of Grade 1 Embryos
Grade 1 embryos demonstrate specific morphological features that distinguish them from lower-quality embryos:
- Equal-sized blastomeres: All cells within the embryo are uniform in size, indicating synchronized cell division 1
- Absence of fragmentation: No anucleated fragments present (ideally <20% fragmentation) 2
- Absence of multinucleated blastomeres: Each cell contains a single nucleus 2
- Appropriate cell number for developmental stage: Four to five blastomeres on day 2, and seven or more cells on day 3 2
Clinical Significance and Pregnancy Outcomes
The quality grading directly correlates with pregnancy success:
- Grade 1 embryos achieve clinical pregnancy rates of 21.8% per embryo transfer, significantly higher than grade 2 embryos (12.8%) or grade 3 embryos (0%) 1
- Implantation rates reach 49% when two top-quality embryos are transferred, compared to 35% with one top embryo and 12% with no top-quality embryos 2
- Embryo quality is the strongest predictor of pregnancy success after controlling for other variables including patient age, with statistical significance (p = 0.0011) 1
Grading System Context
The grading classification typically follows a three-tier system:
- Grade 1: Equal-sized blastomeres with no fragmentation (highest quality) 1
- Grade 2: Unequal-sized blastomeres 1
- Grade 3: Evidence of fragmentation (lowest quality) 1
This morphological assessment is performed on day 2 or day 3 of embryo development and serves as the primary tool for embryo selection in clinical practice 3. The grading scheme evaluates three key parameters: cell number (growth rate), fragmentation, and evenness of blastomeres 3.
Important Clinical Considerations
Despite having Grade 1 embryos, current ESHRE guidelines strongly recommend elective single embryo transfer (eSET) regardless of embryo quality to avoid the substantial risks of multiple pregnancy 4. The decision to transfer multiple embryos should never be based on embryo quality alone, as the 30-fold increased risk of multiple pregnancy with double embryo transfer outweighs any perceived benefit 5.