Stage 3, Early Morula.
A. Quality 1, Excellent. Individual blastomeres of uniform size are still discernible. The cell mass occupies about 60% of the perivitelline space. This embryo was collected on Day 6.5. B. Quality 2, Fair. At least 50% of the cellular material is intact. One large extruded cell is present and three vacuolated cells may be discerned. C. Quality 3, Poor. About 30% of the cell mass appears intact and viable. The mass is accompanied by a number of degenerated cells. D. Quality 4, Degenerate.
Wright JM (2004)