Understanding Embryo Grading

Embryo grading is often one of the most complicated pieces to understand during the surrogacy process. The quality of the embryo is one of several important components involved in the success of an IVF pregnancy. Various pieces of information are used to determine the health of embryos, such as the number of cells present and the overall quality.

Assigning a grade is one way to identify the best quality embryos for the selection of embryo transfer during an IVF procedure. Using this information, decisions can be made about how many embryos to transfer, how many to freeze, and what to do with embryos that are not developing well; but what does this mean about your chances of getting pregnant?

By the third day after fertilization, the embryo should have divided into approximately eight individual cells. These multicellular-stage embryos are then graded based upon the number of cells in the embryo and their appearance under a high-power microscope. While the cell number is objective, the score for appearance is subjective using a score of 1-4.

  • Grade 1. Cells are equal in size without any fragmentation.
  • Grade 2. Cells are equal in size with minor fragmentation.
  • Grade 3. Cells are unequal in size with no fragmentation to moderate fragmentation.
  • Grade 4. Cells are equal or unequal in size with moderate to heavy fragmentation.

Embryos graded 1 or 2 have the greatest potential for developing into a blastocyst, however, grade 3 embryos may also be of good quality if their appearances can be explained by cell division as opposed to poor development. Studies have shown that the number of cells in the day 3 embryo is a better indicator of potential than the grade of the embryo itself; therefore, an 8 cell Grade 3 embryo would have better potential than a 4 cell grade 2 embryo on day three.

The next stage of embryo grading occurs on day five. By this point, embryos continue to divide and the number of cells continues to increase, but the cells are also growing and differentiating into specific cell types: embryo or blastocyst. Day five grades are assigned a number to represent how much it has expanded and a letter to let patients know the quality of the cell – the part of the blastocyst that will become the baby. For example, the highest grade an embryo can receive is 4AA.

  • Grade A. Cells have regular blastomeres and no fragmentation.
  • Grade B. Cells have regular blastomeres and over 10% fragmentation.
  • Grade C. Cells have irregular blastomeres and up to 35% fragmentation.
  • Grade D. Cells have irregular blastomeres and over 35% fragmentation.

Embryo grading is a tool that physicians use in tandem with a Surrogate’s age, medical history, and other information to help determine the optimal day of transfer, the number of embryos to transfer, and exactly which embryo to transfer. Although these grades can be confusing, they are simply helpful guidelines to ensure the smoothest beginning to a happy and healthy pregnancy. If you are seeking additional information on the surrogacy process, contact Surrogate Solutions today!




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