Introduction
Your embryo's quantitative score
Assisted reproductive technology (ART) has been a game-changer in helping couples who are struggling to conceive. However, the success of ART procedures is heavily dependent on the quality of embryos used.
Embryo grading is a system that attempts to standardize the quality of an embryo down to a grade or "score". The Gardner Embryo/Blastocyst Grading System is one of the most widely used grading systems in ART clinics around the world.
Gardner Embryo Grading System
Grading Criteria Used
Development Stage: The development stage of the embryo is determined by the number of cells present at a given point in time. For example, a blastocyst with many cells in the inner cell mass and trophectoderm layers would receive a higher grade than one with fewer cells.
Inner Cell Mass Quality: The inner cell mass is the cluster of cells that will eventually form the fetus. This quality is assessed by its compactness, degree of differentiation, and overall size.
Trophectoderm Quality: The trophectoderm is the layer of outer cells that will eventually form the placenta. This quality is assessed by its organization, thickness, and degree of expansion.
Limitations
the Gardner Embryo/Blastocyst Grading System is widely used and considered a reliable grading system, it does have some limitations. The main limitation is that the grading system is subjective and can vary between embryologists.
The subjective aspect of the grading system means that there is a risk of variability between embryologists, which can impact the accuracy of the grading system. This could lead to embryos being assigned grades that are not reflective of their true quality.
The Number
1-6 indicate the stage or degree of the expansion of the embryo's cavity.
- 1: Early: The blastocele is less than half the volume of the embryo.
- 2: Blastocyst: Greater than or equal to half of the volume of the embryo.
- 3: Full blastocyst: Completely fills the embryo.
- 4: Expanded blastocyst: Volume is larger than that of the early embryo and the zona pellucida is thinning.
- 5: Hatching: The trophectoderm has started to herniate.
- 6: Hatched: Completly escaped from the zona pellucida.
The Letter
The two letters are for the two parts of a day 5 embryo:
- The Inner Cell Mass (ICM) which becomes the fetus.
- The Trophectoderm (TE) which becomes the placenta.
The ICM score is first followed by the TE score.
ICM Score
- A - numerous cells, tightly packed.
- B - several cells loosely packed.
- C - very few cells.
TE Score
- A - many cells, cohesive layer.
- B - few cells forming a loose epithelium.
- C - very few large cells.