Human embryos are defined as human organisms derived by fertilization from 1 or more gametes or diploid cells. Pluripotent stem cells are specialized subpopulation of cells capable of developing into most (ectoderm, mesoderm, and ectoderm), but not all, human tissue and may be derived from human embryos.Given the potential benefits to society, research using human embryos is an issue that deserves additional consideration. The American Academy of Pediatrics believes that, under certain conditions, research using human embryos and pluripotent stem cells is of sufficient scientific importance that the National Institutes of Health should fund it and that federal oversight is morally preferable to the currently unregulated private sector approach.
The 1994 National Institutes of Health (NIH) Human Embryo Research Panel proposed a limit of 14 days after fertilization for the use of embryos for research. Although this limit may appear somewhat arbitrary, which the panel acknowledged, this limit was based on at least 2 important considerations. First, 14 days appears to be the limit after which twinning does not occur. Hence, before this date, it is more difficult to consider an embryo as a distinct, developing individual. Second, 14 days is a period before the development of the primitive streak, which eventually develops into the embryonic neural system. Although some have argued for limiting the use of human embryos in research to earlier or later stages of development, the NIH panel believed that this clearly defined number would address many of the ethical concerns about the use of embryos while allowing research, albeit of limited scope. In effect, this choice reflects an argument that the early embryo before 14 days of development is not the equivalent of a fetus or person and, thus, may be used in research under certain additional conditions. (Annas, Caplan and Elias, 1999)
