Embryo Grading - What does it mean?

Embryo Grading Explained: Why Specialists Look for an 8-Cell Embryo

Shared from IVF Babble

Since school has started back for so many, it seemed like a good time to talk about grades! In our case, embryo grades. Fertility advocate Jennifer Palumbo explains

Embryo grading is an essential part of in vitro fertilization (IVF) treatment. However, it is a complex process, and embryo grading systems are subjective. Nonetheless, specialists have developed standards to determine which embryos to transfer or freeze. One of the most significant indicators of embryo quality is an 8-cell embryo – and here we explain why.

An 8–Cell Embryo and the Quality of Division

The embryo is at the ‘cleavage (not THAT kind of cleavage!) stage three days after fertilization.’ At this stage, the cells in the embryo are dividing, but the embryo itself is not increasing in size. Instead, the genetic material replicates as the cells divide.

Some embryos will divide into two cells, then four, then eight, but others may separate differently, forming an uneven number of cells. Both patterns of cell division are considered normal.

When embryos are graded on day 3, embryologists look for fragmentation. Fragmentation is where small amounts of cytoplasm (the material within the cell) separate from the cells. The embryo is less likely to develop into a good-quality blastocyst if significant fragmentation is observed.

Fertility specialists will grade cleavage stage embryos based on the number of cells and their appearance. Different labs across the country may use other grading systems.

For example, some labs score the day three embryo using a 4-point system. A typically developing day three embryo will contain between 6–10 cells. The embryo grade depends on how the cells in the embryo look under the microscope. A high-quality embryo will have even-sized cells and no fragmentation. According to research, 8 cell embryos are most likely to develop into viable blastocyst embryos. The different grades of an embryo are described below:

● Grade 1 – Cells are equal in size, and there is no fragmentation.

● Grade 2 – Cells are equal in size with very little fragmentation.

● Grade 2.5 – Cells are equal, with moderate fragmentation.

● Grade 3 – Cells are unequal, with little or no fragmentation

● Grade 4 – Cells are unequal, and fragmentation is moderate to severe.

Why embryo grading is useful

While it may feel like it’s just to torture you, embryo grading does have a purpose! Fertility specialists generally regard the top embryo grades as having the greatest potential to develop into the blastocyst stage.

However, lower-grade embryos may lead to high-qualityblastocysts. For example, research shows that the number of cells in a day 3 embryo is a better indicator than embryo grade. As such, a day 3, 8-cell embryo has greater potential than a 4-cell grade 2 embryo on day 3. Nonetheless, it is important to remember that embryo grading is indicative; it is a tool that embryologists use alongside a patient’s age, medical history, and other information to determine which embryos to transfer.

Some studies show that higher-graded embryos have better pregnancy rates and more live births, while lower-graded embryos result in poorer pregnancy rates and fewer live births. However, this is not the case for all embryos.

Bottom line: It’s hard to know, based on grading alone, what your success will be. Embryo grading is one step in a journey that may often seem endless. Your fertility team considers other factors when they decide to transfer: your age, fertility history, which embryos to transfer, how many embryos to transfer, and which day will most likely lead to a successful pregnancy.