You might be wondering how embryo grading affect the chances of your pregnancy. The whole process can be complex.
Under a microscope, embryologists mainly assess an embryo quality during an in-vitro fertilization (IVF) to determine the optimum embryo to transfer, the most appropriate day of embryo transfers, and the number of embryos to transfer.
However, it is important to consider that the results of embryo grading can be subjective. There are instances where low-graded embryos lead to positive pregnancies while perfect embryos do not. Other factors such as uterine receptivity, genetic health, and lifestyle quality can also influence IVF success rate.
So does IVF embryo grading still matter? The answer is yes. It helps identify those most likely to implant for an IVF treatment. To understand what this means for an embryo’s development, let’s explore how embryo grades influence IVF success rates.
How Are Embryos Graded?
Our embryologist at Fertility Philippines grade embryos through two stages: Day 3 (cleavage stage) and Day 5 or 6 (blastocyst stage). The quality of embryos develop differently on these days, which can help determine the best embryo quality to transfer or freeze for preservation.
Day 3 or Cleavage Stage Embryo
At the cleavage stage, embryos are dividing but are not growing in size. They typically consist of 6 to 8 cells within an outer shell called zona pellucida (ZP). Day 3 embryos with more than 6 cells are more likely to develop into a quality blastocyst than embryos with fewer cells.
In some instances, a small portion of cytoplasm (inside of the cell) can break off after a cell divides and forms a fragment that deprives an embryo of essential organelles and regulatory proteins to fully develop.
When an embryo contains excessive fragmentation, the cells lose too much cytoplasm, causing developmental disadvantages like reduced implantation potential and failed pregnancy.
To grade cleavage stage embryos, we use the number of cells in the embryo and their appearance under a microscope. The cell numbers are objective but the appearance is graded from 1 to 4. For instance, a grade one embryo has cells with the same size and no fragmentation seen.
We use the following guide to grade embryo appearance:
| Cleavage Stage Embryo Grade | Description |
| Grade 1 | Cells with equal size and no fragmentation. |
| Grade 2 | Cells of equal size with minor fragmentation. |
| Grade 2.5 | Most cells are in equal size with moderate fragmentation. |
| Grade 3 | Cells are unequal in size with no to moderate fragmentation. |
| Grade 4 | Cells with moderate to heavy fragmentation. |
Although grades 1 to 2.5 may seem to have the best potential to turn into a blastocyst, grade 3 can still be a good quality if its appearance is based on asynchronous cell division rather than poor growth.
On day 3, a grade 3 embryo with 8 cells can have a better potential than a grade 2 embryo with only 4 cells.
Day 5 or Blastocyst Stage
During the blastocyst grading, two cell types will form. The first one is the inner cell mass (ICM) that grows into a fetus, while the trophectoderm epithelium (TE) that generates tissues needed for pregnancy. These two produce a fluid filled sphere called blastocoel, with TE as the outer layer of the ICM inside.
Day 5 embryos will be graded based on the blastocyst stage of expansion, ICM, and TE quality. The blastocoel will be assessed on a scale of 1 to 6, with 6 being the highest level of expansion.
| Blastocyst Stage Embryo Grade | Description |
| Grade 1 | In early blastocyst, the blastocoel is less than half of the embryo. |
| Grade 2 | A blastocoel volume becomes more than half of the embryo. |
| Grade 3 | The blastocyst is full with the blastocoel filling the embryo. |
| Grade 4 | An expanded blastocyst has a thinning ZP with the blastocoel larger than the embryo. |
| Grade 5 | A hatching blastocyst has a TE bursting through the ZP. |
| Grade 6 | When a blastocyst hatches, TE fully burst through ZP. |
Our system grades embryos through letters. A high-graded embryo with an optimal development and minimal abnormalities can be labeled as “AA.” The first letter represents ICM and the second letter indicates the TE quality, potentially becoming the placenta.
- AA or AB: Indicates high potential of successful implantation and fetal development.
- BB or BC: An average quality embryo with moderate chances of success.
- CC or lower: Suggests a lower potential for successful implantation.
Below shows you the embryo grades with the poorest and best results.
What an Embryo Grade Doesn’t Tell You
It is important to remember that a high-grade embryo may still have chromosomal abnormalities, while an average embryo may be genetically normal. This is why some patients combine embryo grading with genetic testing (PGT-A Testing) for a more comprehensive picture of an embryo’s viability.
Also, an embryo with A grade ICM may be better than a C but a C can still develop into an A or B later on. Similarly, expansion grades can grow over time. There is a possibility that an early blastocyst on day 5 becomes an expanded blastocyst by day 6. This means that determining the potential of an embryo requires an evaluation of all its components.
Embryo grading does not always guarantee a successful pregnancy. It is a tool that embryologists use to track embryo development in a lab for 3 to 7 days. It is used in conjunction with a patient’s age, fertility history, and other information to identify the best course of action in predicting pregnancy before implantation.
How can Embryo Grading support your IVF Treatment?
Understanding embryo grading can make the IVF process less overwhelming and more transparent. While embryo grades set expectations, they are only a small part of the whole picture.
The grades can guide both patients and fertility specialists to improve the chances of a successful, healthy pregnancy.
At Fertility Philippines, we are here to walk you through your IVF journey from your embryo selection to implantation. Consult us to begin your fertility treatment today.