Understanding Embryo Grading for Intended Parents
Once your embryos have been created your first question to the doctor may be, “How good do the embryos look?” The answer you receive is typically referred to as the embryo’s “grade.” For many intended parents, the answer might as well be delivered in a foreign language. IVF is likely very new to you, and being told that your embryos are a 2.5 may not do much to answer your original question.
Embryo grading is determined by several factors, the first being the day in which the grade is given. Grades are typically delivered on either day three or day five of growth. Because the degree to which the embryo has developed differs drastically from day three to day five, the method for grading will differ as well.
Day 3 Grading
During this phase of development the cells divide rapidly. You should note that a dividing cell, in this phase of development, is not a growing cell. All cells at this stage will be roughly the same size, but the number of divisions within the cell may vary greatly.
As the cells divide, occasionally some of the cytoplasm, the inside of the cell, will break off and form smaller “fragments” that do not contain a nuclei and are not considered a true “cell.” These fragments occur naturally and do not immediately suggest poor embryo quality.
Day 3 cells are graded based on the number of cell divisions visible relative to the number of fragments that are visible. Typically doctors hope to see between six and ten equally sized cells and an absence of fragments in an ideal day 3 embryo.
The grading scale will continue to look at cell divisions and fragmentations and assign a numerical grade between 1 and 4. Doctors expect embryos with a grade of 1- 2.5 to have the most likely chance of continuing to develop into a day 5 blastocyst.
Day 5 Grading
Most doctors will wait to issue a grade until the embryo reaches the blastocyst stage on day 5 of development. While cells are continuing to divide, they are now also growing in volume. This means that they may outgrow their “shell” and begin to hatch in preparation for implantation into the uterine lining.
Another part of development on day five is that there are now two types of cells present. The inner cell mass (ICM) which will eventually turn into the fetus, and the Trophectoderm Epithelium (TE) which will eventually form necessary tissues needed for pregnancy, including the placenta. Doctors will be looking for both types of cells and as judging their appearance when issuing a day five embryo grade. Other considerations include the fluid cavity between the two cell types and how much the embryo has expanded.
Once they’ve finished evaluating the embryo, doctors will issue a letter grade to the blastocyst. Most doctors will issue a grade for each type of cell, resulting in a two letter grade. Other doctors will also give a third letter grade to correspond with the growth. As a result, the best quality day five embryo will receive a grade of “AAA” or “AA.”
Doctors then consider the grading of each component of the cell when deciding if they believe the embryo is likely to continue growing and result in a positive pregnancy. The grading system at this stage can be quite subjective and is therefore not a guarantee. Even the best graded embryos may fail to implant and grow while, occasionally, embryos with a lower grade may develop into a healthy pregnancy. It is important to remember that grading is just a tool, not a promise of success.
If you find that you still have additional questions on embryo grading or how to understand the grading system, don’t be afraid to speak with your Case Specialist or IVF doctor.