Understanding Embryo Grading
What is Embryo Grading?
Embryo grading is a standardized way of assessing the quality of embryos based on their appearance under a microscope. While grading systems vary slightly between clinics, most use a combination of letters and numbers to categorize embryos. This grading helps embryologists determine which embryos have the best chance of implanting and developing into a healthy pregnancy.
Embryo grading is typically done on day 3 and day 5 or 6 of development. Each stage offers different insights into the embryo’s potential viability.
Day 3 Embryo Grading
On day 3, embryos are at the cleavage stage, meaning they consist of several cells that continue to divide. The grading at this stage focuses on:
Number of Cells: A high-quality day 3 embryo typically has 6–8 cells.
Fragmentation: Embryos with minimal fragmentation (tiny bits of cytoplasm breaking off) are preferred.
Cell Uniformity: Evenly sized and shaped cells are considered higher quality.
A common grading system for day 3 embryos uses numbers and letters, such as 8A or 6B:
The number represents the number of cells.
The letter (A, B, C, or D) indicates the quality, with A being the best (evenly sized cells, minimal fragmentation) and D being the poorest quality.
Day 5/6 Embryo Grading (Blastocyst Stage)
By day 5 or 6, the embryo reaches the blastocyst stage, which is when it has divided into two main structures:
Inner Cell Mass (ICM): This part will develop into the fetus.
Trophectoderm (TE): This part will become the placenta.
A typical grading system for blastocysts includes three components, such as 5AA, 4BB, or 3AB:
The first number (3–6) represents the level of expansion, with 5 or 6 being fully expanded blastocysts.
The first letter (A, B, C) grades the inner cell mass (ICM)—A is the best.
The second letter (A, B, C) grades the trophectoderm (TE)—again, A is the best.
Does a Higher Grade Mean a Guaranteed Pregnancy?
While higher-graded embryos statistically have a better chance of implantation, grading is not a definitive predictor of success. Many lower-graded embryos result in healthy babies, while some higher-graded embryos may not implant. Other factors, such as genetic health, uterine receptivity, and overall embryo development, play crucial roles.
Why Embryo Grading Matters
Embryo grading helps embryologists select the most viable embryos for transfer, increasing the chances of pregnancy. However, it’s just one piece of the puzzle—genetic testing (PGT), maternal health, and the quality of the uterine environment all contribute to success.
Final Thoughts
Understanding embryo grading can provide clarity and comfort during an often-overwhelming process. It’s important to discuss grading results with your fertility specialist to set realistic expectations and determine the best approach for your unique situation. Regardless of the grade, every embryo holds potential, and every fertility journey is unique.
Watch the video below to see the incredible moment of fertilization—it's amazing to witness life begin!
