In human embryonic development, a pre-embryo is a conceptus before implantation in the uterus.[1]

Pre-embryo in human embryonic development

See also: Zygote § Humans

The word pre-embryo sometimes is used in ethical contexts to refer to a human conceptus at least between fertilization and implantation, though this term has not been adopted by the scientific community.[2] A conceptus between fertilization and implantation is also frequently classified as a pre-implantation embryo.[2]

Even after implantation begins, a pre-embryo may exist up until formation of the primitive streak.[3] Implantation begins at about six days after fertilization, and lasts for about a week, during which time formation of the primitive streak occurs.[4]

Use of the term pre-embryo, in the context of human development, has drawn criticism from opponents of embryo research, and from scientists who have considered this categorization invalid or unnecessary.[1][5][6] One rationale that has been advanced for distinguishing an early fertilized human conceptus from an embryo is that there is a potential for the conceptus to split into identical twins prior to implantation, and so (the argument goes) the conceptus cannot be regarded before implantation as a single human being. However, the conceptus before implantation exhibits self-actuated activity, which has led to the assertion that it is an embryo.[7] Further, identical twinning is an instance of asexual reproduction whereby a conceptus, without ceasing to be what it is (a new human being), provides a cell or cells as a new conceptus, entirely separated or partially separated (a 'siamese' twin) from the original conceptus, but in any event self-actuated in its development from the moment that the act of asexual reproduction (twinning) is complete.[citation needed] By this asexual reproduction, the parents of the original conceptus in effect become grandparents to the identical twin so conceived.[citation needed]

In the United States, a report by the National Institutes of Health stated that a conceptus could be both a pre-implantation embryo and a pre-embryo at the same time.[8] However, Ann Kiessling (a leader in stem cell research) has written that those categories are inaccurate.[9]

Ontological status

The ontological status of the proembryo, embryo, and fetus

The illustration shows the ontological status of the preembryo, embryo, and fetus:

The colors represent the maternal and paternal genetic contributions.

See also

Footnotes

  1. ^ a b Spallone, Patricia. “Bad Conscience and Collective Unconscious: Science, Discourse and Reproductive Technology” in Rosenbeck, Bente et al. Forplantning, køn og teknologi, pages 131-132 (Museum Tusculanum Press 1995).
  2. ^ a b Dyson, Anthony and Harris, John. Ethics and Biotechnology, page 94 (Routledge 1994).
  3. ^ Pickering, Neil and Evans, Donald. Creating the Child, page 39 (Martinus Nijhoff Publishers 1996).
  4. ^ Steinbock, Bonnie. “Life Before Birth,” pages 50 and 214-215 (Oxford University Press 1992).
  5. ^ Mulkay, Michael. The Embryo Research Debate, page 31 (Cambridge University Press 1997).
  6. ^ Braude, Peter. “Preimplantation Genetic Diagnosis and Embryo Research-Human Developmental Biology in Clinical Practice,” International Journal of Developmental Biology, volume 45, page 607 (2001).
  7. ^ Ashley, Benedict and O’Rourke, Kevin. Ethics of Health Care: An Introductory Textbook, page 127 (Georgetown University Press 2002).
  8. ^ Report of the Human Embryo Research Panel of the National Institutes of Health Archived 2009-01-30 at the Wayback Machine (1994).
  9. ^ Kiessling, Ann. What is an Embryo?” Connecticut Law Review 36 (4): 1051–93.
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