A woman’s jou rney up until transfer day focuses on the development of her lining. Doctors consider how thick it has become, if a triple stripe pattern is present, and if there is any fluid in the uterine cavity. But on transfer day everything shifts. The emphasis now becomes the quality of the embryos. On transfer day you may hear a new term: “Embryo Grading.”
Embryo grading is a tool developed to answer the frequently asked question, “How healthy do the embryos look?” Unfortunately, the answer may as well be delivered in a foreign language. IVF is likely very new to you, and being told that the embryos are a 2.5 may do little to nothing to answer your original question.
Embryo grading is assigned based on 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. Given the fact that how the embryo is growing differs drastically from day three to day five, the method for grading differs as well.
Day 3 Grading
During this phase of development, the cells are dividing rapidly. You should note that a dividing cell in this phase of development is not growing. 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, it is worth noting that 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 are not abnormal and do not immediately suggest poor embryo quality.
Day 3 cells will be graded based on the number of cell divisions visible in contrast to the number of fragments that are visible. Typically doctors hope to see between six and ten equally sized cells and no 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.
A new 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 look for both types of cells and judge their appearance when issuing a day five embryo grade. Other issues of note 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 issue a grade for each type of cell, resulting in a two-letter grade. Other doctors also give a third letter grade to correspond with the growth. As a result, the best quality day five embryos receive a grade of either “AAA” or “AA.”
Doctors then consider the grade 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 that grading system, don’t be afraid to speak with your Case Specialist or IVF doctor.