During in vivo development, maternally and embryonic-derived growth factors play a role in preimplantation development. The addition of growth factors to culture medium for human pre-implantation development has had beneficial effects on embryo development and quality. Examples of some of the growth factors that have proven to have beneficial effects are: granulocyte macrophage colony stimulating-factor (GM-CSF), epidermal growth factor (EGF), insulin-like growth factors (IGF), leukemia inhibitory factor (LIF), platelet activating factor (PAF), and platelet-derived growth fact (PDGF). Culture of human embryos in the presence of GM-CSF has shown increased rates of blastocyst formation as well as total number of cells allocated to the inner cell mass (ICM) and trophectoderm. A factor that is unique in terms of clinical application in assisted reproduction is hyaluronan. The culture media formulations in use today contain the necessary substrates in order to support the development of competent blastocysts.