Stage 4, Morula.
A. Quality 1, Excellent, symmetrical embryo free from imperfections. Individual blastomeres may still be identified when focusing up and down. The outline of the embryo has scalloped edges. The cell mass of about 64 cells occupies approximately 80% of the perivitelline space. The zona pellucida is intact. Collected on Day 7. B. Quality 2, Fair. The cell mass still exceeds 50%. Several extruded cells are evident. C. Quality 3, Poor. Only about 25% of the intracellular cell mass appears to be intact and viable. There are a few extruded blastomeres and the remainder is fragmented material. D. Quality 4, degenerate embryo. There appear to be remnants of small blastomeres. The cellular material has degenerated and is non-viable. Collected on Day 6.
Wright JM (2004)