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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.
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