Stage 7, Expanded Blastocyst.
A. Quality 1, Good. The blastocele is clear for the most part and the intercell mass is well defined. The zona pellucida is thinner due to the expansion. B. Quality 2, Fair. The intercell mass is not well delineated which may be due extruded cells pressed against the zona pellucida. C. Poor. There is no clearly defined intercell mass. D. Degenerate. Cellular material has disintegrated and the embryo has collapsed within the perivitelline membrane.
Wright JM (2004)