Embryo Grading Explained: What 4AA Really Means
Your embryology report may include codes like 4AA, 3BB, and Day 5. Here is a practical guide to what those terms often mean.
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The Gardner Grading System (Day 5 Blastocysts)
Most clinics use the Gardner scale, which consists of a number and two letters (e.g., 4AA).
1. The Number (Expansion)
Describes how expanded the blastocyst is (1-6).
- 1-2: Early blastocyst (cavity is forming).
- 3: Full blastocyst (cavity fills the embryo).
- 4: Expanded blastocyst (cavity is larger than the original egg).
- 5: Hatching (cells are starting to break out of the shell).
- 6: Hatched (embryo has completely left the shell).
2. The First Letter (Inner Cell Mass)
Grades the inner cell mass, the group of cells that can develop into fetal tissue.
- A: Many cells, tightly packed.
- B: Several cells, loosely grouped.
- C: Very few cells.
3. The Second Letter (Trophectoderm)
Grades the trophectoderm, the cells that can contribute to placental tissue.
- A: Many cells forming a cohesive layer.
- B: Few cells forming a loose layer.
- C: Very few large cells.
Related Resources
Common Questions
Is a 'C' grade embryo bad?
Not necessarily. Visual grades describe appearance under the microscope and do not decide the outcome by themselves. Ask your clinic how they interpret the grade alongside age, embryo day, PGT-A results if used, and your treatment plan.
What is the difference between Day 3 and Day 5?
Day 3 embryos are usually in the cleavage stage, while Day 5 embryos are usually blastocysts. Clinic preferences vary by protocol, embryo development, and patient history.
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