This quality depends on intrinsic characteristics of the embryos but also on the cultures conditions. Different culture systems and media can be used. Complex media Amino-acids and vitamines are added. Since the nutritive requirement of the embryos changes in function of their stage of development, culture is performed in different media according to their cleavage stage. Although beneficial, the mechanism of action of these cells is not well known.
Some groups transfer embryos at the blastocyst stage.