Embryo Assessment, Grading, and Selection
Core concepts
Assessment combines morphological grading (cell number, symmetry, fragmentation, compaction, blastocoel expansion, inner cell mass and trophectoderm quality) with developmental timing. Know common grading schemes and what each parameter reflects. Time-lapse imaging adds kinetic information but does not replace morphological assessment.
Selection principles
Selection aims to identify the embryo with the highest implantation potential. Consider day of development, morphology, and patient factors. Genetic testing (PGT) is a separate selection tool with its own indications and limitations.
Traps
- Assuming a higher grade guarantees implantation.
- Confusing fragmentation (cytoplasmic blebs) with vacuolization.
- Overweighting a single parameter such as cell number.
- Forgetting that grading schemes vary between labs and are not universally standardized.
Rule of thumb
"Grade is a probability, not a promise." When comparing embryos, weigh developmental stage and morphology together; a slightly lower-grade blastocyst on the correct day may outperform a higher-grade arrested embryo.