For those undergoing in-vitro fertilization (IVF) therapy in Ontario, an embryo grading chart explains the grades of the available embryos. The quality of the embryos is a major factor in the success of IVF treatment. As 60% of miscarriages are caused by embryo irregularities, using the highest quality embryos can lead to a healthy and safe IVF success story.
What Is Embryo Grading?
Embryo grading is a method used by IVF specialists to better understand which embryos to use, how many to use, and when to perform the embryo transfer. This is key to narrow down the optimal time as well as the highest quality embryos. The transfer of an embryo is done on Day 3 or Day 5 once a retrieval is completed. Understanding the difference in the days can help make an informed decision.
Day 3 Embryo Grading of Cleavage Stage Embryos
On day 3 of the embryo grading, the embryos are called cleavage stage embryos, as the embryo divides, not grows in size. The structure of the embryo is viewed with a microscope to verify the number of cells it contains, and the appearance of the embryo is reviewed. A promising embryo should have six to 10 cells. The appearance of the cells is deemed another factor in success as any cell that loses too many contents may not thrive. The division process can play a role as the embryo is graded depending on the result. For example, a Grade A embryo has six to 10 uniformed-size cells with a fragmentation of less than 10%. Grade B is assigned to embryos with an irregular shape and a fragmentation ranging from 25% to 50%. Embryos with a fragmentation of more than 50% are Grade C.
Day 5 Embryo Grading of Blastocysts
With day 5 embryos, they are referred to as blastocysts. At this stage, the embryo is graded based on three factors: the degree of expansion (within the cavity), the appearance of the inner cell mass, and the appearance of the trophectoderm. This grading system is more complex than day 3 grading. As the cells divide, increasing the numbers, they begin to develop into two different types. One group of cells form the Inner Cell Mass (ICM), which in time forms the fetus. The other groups of cells join to form a layer of cells that develop into the trophectoderm epithelium (TE). These cell types create the placenta and other tissues needed throughout the pregnancy. The two types of cell groups work together to form a sphere to protect the fetus. The fluid-filled globe develops with the ICM on the inside and the TE cells forming the outer layer. The division of all cells ending in this result provide the start of the pregnancy.
The Embryo Grading Chart
Many fertility clinics use a basic grading chart to determine the sizes and condition of the cells. The day 3 embryos can be marked as numbers or letters, depending on the facility. Grade 1 cells equal the above-mentioned Grade A while Grade 4 is parallel with Grade D. A common Day 3 embryo grading chart can be presented as such:
- Grade 1 or A: Cells are uniformed with no fragmentation
- Grade 2 or B: Cells are uniformed with minor fragmentation
- Grade 3 or C: Cells are similar sized with moderate fragmentation
- Grade 4 or D: Cells are either uniformed or not with moderate to heavy fragmentation
With the day 5 blastocyst grading factors, the embryos are arranged by a number referencing the expansion stages of the cell, and two letters. The first letter signifies the ICM and the second represents the TE cell grade. The number for the blastocyst expansion is measured as:
- Grade 1: Blastocoel cavity is under half of the volume of the embryo
- Grade 2: Cavity is more than half of the volume of the embryo
- Grade 3: Cavity fills the embryo
- Grade 4: Cavity is more than the volume of the embryo as the membrane thins
- Grade 5: TE begins to expand through the membrane
- Grade 6: TE completely erupts the membrane
The first letter, representing the Grade of ICM, is measured as:
- Grade A: Solid layer of cells
- Grade B: Freely packed cells
- Grade C: Few large cells
The second letter, representing the Grade of TE, is measured as:
- Grade A: Solid layer of cells
- Grade B: Loose layer of cells
- Grade C: Few cells
The Importance of Embryo Grading
The grading guide is used in fertility clinics across Ontario to determine which embryos have the best chance for a successful pregnancy. As a major contributing factor, the grading of the embryo cells is not the only influence for an effective treatment. The grading is used along with the ages of the patients involved, their medical history, and of any knowledgeable cause for infertility.
Success Rates by Grade
When measuring success by the grading scale, it shows that embryos falling in the highest category provide a 65% success rate. An average grade can see a 50% pregnancy rate with a low rating offering less than 33% success. The grading of the embryos is not a clear-cut solution to fertility problems. It is important to remember what may be measured as a low-quality letter or number as a day 3 embryo cell may develop into a more promising cell on the grading scale by day 5. In fact, many studies have proven that with two frozen embryos, one of a higher grade compared to the other, the “superior” is not always the most successful. In some cases, the predicted success of the higher graded embryo has seen to not fully develop while the lower graded embryo resulted in a live birth.
Fertility Assessment Solutions at ONE Fertility Kitchener Waterloo
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