How to grade an embryo?

1The EQC test will present you several possible answers for the various characteristics of an embryo. You can make only one choice. You are certainly used to grade the embryos in your day-to-day activity, grading is a convenient way of communicating embryo characteristics both to colleagues and medical staff. In our view, this is an important parameter to monitor in an External Quality Control scheme.



Number of blastomeres

The first mitotic division usually occurs between 20-24 h after fertilization. Cleavages will then continue

Parameters        Morphological aspect
2 – 16 nomber of blastomeres clearly identifiable in an uncompacted embryo

Blastomere sizes

Embryos usually cleave giving rise to blastomeres of equal sizes. Usually, the mitotic divisions occurs in an asynchronous manner in each blastomere. In embryos with 2, 4, 8 or 16 blastomeres the sizes of each cell should ideally be equal, but this might not always be the case. In embryos with uneven blastomeres (3, 5, 7, 9, 11, 13, 15) or in those containing a number of blastomeres that is not a multiple of 4, the sizes should also be different.

Parameters Morphological aspect
Equal the blastomeres are of equal sized
Unequal the blastomeres are of unequal sizes


During development of the embryo, some blastomere may expel some material, known as fragments. These fragments may vary in amount and size from one embryo to the other. Ideally, no or very little amount of fragments is visible. In extreme case, the fragments may occupy almost all space within the zona pellucida.

Parameters             Morphological aspect
0% no fragments appear between the blastomeres
<10% the volume occupied by the fragments is less than 10% of the total embryo volume
10-<25% the volume occupied by the fragment is more than 10%, but less than 25%
25-<50% the volume occupied by the fragment is greater than 50%