Embryo Grading Explained

Q: What does embryo grading mean in IVF?

Embryo grading is the visual assessment of embryo quality. At the blastocyst stage, the most common system evaluates expansion (1-6), inner cell mass quality (A-C), and trophectoderm quality (A-C). A grade like 4AA represents a fully expanded blastocyst with excellent inner cell mass and trophectoderm.

Q: Does embryo grade predict IVF success?

Higher grades correlate with higher implantation rates at the population level, but grade is not determinative for individual embryos. A top-grade embryo can fail to implant if chromosomally abnormal. A lower-grade embryo can result in a healthy pregnancy.

Bottom line

Embryo grading is a morphological assessment performed by embryologists to evaluate blastocyst quality. The Gardner system scores three dimensions: expansion stage (1-6), inner cell mass quality (A-C), and trophectoderm quality (A-C). Higher grades correlate with higher implantation rates at population level, but lower-grade embryos can and do produce healthy pregnancies. Grading does not assess chromosomal status.

Reviewed byIVF Daddies Editorial· Clinical Embryology

What Grading Measures

Embryo grading is performed by embryologists using microscopy. At the blastocyst stage (day 5–7 after fertilization), three characteristics are assessed:

Expansion (number 1–6):how fully the blastocyst cavity has expanded and whether it has begun hatching.
Inner Cell Mass, ICM (letter A to C):the cluster of cells that will become the baby.
Trophectoderm, TE (letter A to C):the outer cell layer that will become the placenta.

Expansion Stage Reference

1

Early blastocyst. Blast cavity less than half the embryo volume.

2

Blastocyst: cavity occupying half or more of embryo volume.

3

Full blastocyst: cavity filling the embryo.

4

Expanded blastocyst. Cavity larger than original embryo; zona pellucida thinning.

5

Hatching blastocyst. Trophectoderm beginning to break through zona.

6

Hatched blastocyst. Fully emerged from zona pellucida.

ICM and TE Grade Reference

Grade	Inner Cell Mass (ICM)	Trophectoderm (TE)
A	Many cells, tightly packed	Many cells, cohesive epithelium
B	Several cells, loosely packed	Few cells, loose epithelium
C	Very few cells	Very few large cells

What Grading Does Not Tell You

Embryo grade is a morphological proxy. It describes appearance, not chromosomal integrity:

Grade does not equal euploid:a 5AA embryo can be chromosomally abnormal.
Lower grade does not equal failure:3BC embryos can and do produce healthy pregnancies.
Grading is observer-dependent:embryologists at different labs may grade the same embryo differently.

Related reference

Preimplantation Genetic Testing (PGT) →Egg Quality Explained →Clinical Embryo Grading (Deep Dive) →← Back to Fertility Explained

This content describes clinical mechanisms for educational purposes. It does not constitute medical advice.