Grading the embryo during IVF may help identify which embryos are more
likely to implant. Many IVF clinics grade the embryos using a scoring
system. Unfortunately, no 2 IVF centers agree on exactly the same grading system and it is a very subjective way to evaluate embryo quality.
Many IV centers assess the "quality" of embryos from in vitro fertilization is by determining 3 major components.
- Cell number
- Cell regularity (regularity of size), and
- Degree of fragmentation.
There are also other things that are also noted about the embryos appearance, such as multinucleation, presence of vacuoles, granularity, thickness of the shell around the embryo, etc.
In general, the lower the grade (1 is better than 2, 2 is better than 3, etc) the higher the chance of getting pregnant.
Below is one grading system of many:
Grade 1 - The embryo should have the appropriate cell number for stage of development (eg., on day three, embryos should have 8 cells, also known as blastomeres). Blastomeres should be even in their size and shape, and embryos should have little or no fragments (small amounts of extracellular debris) between cells.
Grade 2 - Should also have correct development of cell numbers (6-8 cells on day three), may have a small amount of fragmentation (<20% fragmentation), and may have slight uneveness of blastomere sizes.
Grade 3 - Blastomeres are uneven in size, more than 30% fragmentation, and may have normal number of blastomeres, but due to the other factors receives a lower grade. Also, embryos behind in their development (a 4-cell embryo when it should have 8-cells, for example) will also receive a grade of 2 or 3 even if they are normal otherwise.
Grade 4 - Very few, if any, viable appearing cells. Usually a high percent fragmentation (over 50%). Some embryos may fragment completely.