Embryos at the six-cell level are better quality embryos.
There are four grades for evaluating the quality of in vitro embryos; first and second grade embryos are of better quality, third grade embryos can be transferred but may be of slightly poorer quality, and fourth grade embryos are not recommended for transfer.
Grade 1 embryos have almost equal cell size, are transparent, and have a grain-free cytoplasm with little debris. Grade II embryos have slightly different cell sizes, granular cytoplasm, and more debris. Grade III embryo cells are significantly uneven in size, cytoplasmic granulation is evident, and there is a lot of debris. Grade four embryos have severely uneven cell sizes, severe cytoplasmic granulation, and extreme fragmentation.
Six-cell grade one embryos are better embryos and can be used for transfer, which should be done under the supervision of a physician.