title: The early development of human embryos.
abstract: The development of the human embryo from the time of fertilization through the eighth post-fertilization week is described for medical policy purposes. During pre-implantation stages, differentiation occurs between precursors of embryonic and extra-embryonic structures. During implantation formation of a fore-hind axis begins within the inner cell mass. By the end of the eighth week, head, face, hands, and feet are suggestive as to species-recognition but not yet definitive. Data from laboratory studies of non-human mammalian embryos elucidate important aspects of human embryonic development.
mesh_terms: D000818:Animals; D033421:Beginning of Human Life; D001755:Blastocyst / Q000166:cytology; D002970:Cleavage Stage, Ovum; D010064:Embryo Implantation; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology*; D047108:Embryonic Development; D005260:Female; D005306:Fertilization; D005865:Gestational Age; D040821:Human Characteristics; D006801:Humans; D019369:Life; D033261:Maternal-Fetal Relations; D028723:Personhood; D011247:Pregnancy