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A Patient's Guide to Embryo Grading

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.

It is important to realize that most patients can have all of one grade type, but usually have several embryos from different grades. Also, having poor embryo quality does not mean that pregnancy won't occur, just as having all grade 1 embryos does not mean a certain pregnancy. It is known that having grade 1 embryos show a trend toward higher pregnancy rates, while patients having embryos in the grade 3-4 range may become pregnant, but at a lower rate. Embryo grading helps us detemine how many embryos to transfer, and also may also be diagnostic by showing us that embryos are either normal or abnormal in appearance, which may sometimes give a clue to infertility. Finally it is important to remember that embryo grading is subjective, and that IVF programs may vary somewhat in assigning grades to embryos, so it is important to address questions to the Laboratory Director or Reproductive Endocrinologist in the program in which you are being treated.