Stage 5, Early Blastocyst.
A. Quality 1, Excellent. The lightened area is a blastocele. The embryo is symmetrical and free from imperfections. The cell mass almost completely occupies the entire perivitelline space. B. Quality 2, Fair. About 75% percent of the cellular material is intact and viable. The outline of the embryo is irregular in the area of the blastocele. C. Quality 3, Poor. There is evidence of a blastocele and there appears to be an intact embryonic mass of 25%. A 3-dimensional image by virtue of focusing up and down under the microscope would aid in the evaluation of this embryo. D. Quality 4, degenerate. There are several early stage asynchronous blastomeres. All four embryos were collected on Day 7.
Wright JM (2004)