Grade 1 embryos: uniform cell size, regular morphology, intact zona pellucida, uniform and clear cytoplasm, no granulation; between 0-5% fragmentation. Grade 2 embryos: slightly uneven cell size, slightly irregular morphology; cytoplasm may have granular phenomenon; debris between 10-20%. Grade 3 embryos: cells are obviously uneven in size and may have obvious irregularities in shape; cytoplasm may be granular; debris between 21-50%. Grade 4 embryos: cells are severely heterogeneous in size, cytoplasm may be severely granular; fragmentation is above 50%. Generally speaking, grade 1 and 2 embryos have good potential for implantation, grade 3 embryos have diminished potential for implantation, and grade 4 embryos have little or no ability to implant. However, it is important to recognize that the embryos are observed and scored only for a short period of time during embryonic development. The morphology of the embryo may vary considerably at different times.