Human embryo is a human embryo, not a pre-embryo

Objectives: The aim of the study was to investigate the scientific evidence underlying the progressive introduction of the new term “preembryo” in the literature concerning in vitro fertilization and applied preimplantation genetics. Study Methods: Four approaches to the study of the developing human embryo were considered: genomics, DNA expression, cytologyicytogenetics, and cell differentiation. The relevant recent biomedical literature (1985.1999) was collected and critically examined for the presence of molecular, cytological or hystological data suggesting a documented discontinuity in the development’s process or a significant biological novelty concerning the identity of the newly generated organism. A comparative approach (non-human mammalian development) was also adopted to fill the gap in some investigations concerning the human embryo. Results: No relevant data were found supporting the hypothesis of a genomical or cytological discontinuity between the embryo’s organism at any stage of preimplantation development and the same embryo’s organism during or after the implantation process. Unless the exceptional case of monozygotic twinning, in which a new organism is generated from an existing one, any single formed human embryonic organism is genomically and cytologically related to the same organism through the cell cycle events. Since the fusion of the two gametes, the zygote is no more cytogenetically working as a maternal cell, even is some time is required before the full expression of the new genome takes place. This temporal condition appears to be the genetic rule of any development during the life of the human organism, and does not represent a characteristic of the early embryo. Conclusions: The distinction between a stage of human development called “pre-embryo” and a stage called “embryo” (proper) is surreptitious since it does not rest on solid scientific evidence of any kind. Therefore it should be dropped out.