human embryonic development Human embryonic development, or human embryogenesis, is the development and formation of the human embryo. It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of de ...

a pre-embryo is a

conceptus A conceptus (from Latin: ''concipere'' to conceive) is an embryo and its appendages (adnexa), the associated membranes, placenta, and umbilical cord; the products of conception or, more broadly, "the product of conception at any point between fert ...

before implantation in the uterus.

Pre-embryo in human embryonic development

The word pre-embryo sometimes is used in ethical contexts to refer to a human

at least between

fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...

and implantation, though this term has not been adopted by the scientific community. A conceptus between fertilization and implantation is also frequently classified as a ''pre-implantation embryo''.Dyson, Anthony and Harris, John.
Ethics and Biotechnology
page 94 (Routledge 1994). Even after implantation begins, a pre-embryo may exist up until formation of the

primitive streak The primitive streak is a structure that forms in the early embryo in amniotes. In amphibians the equivalent structure is the blastopore. During early embryonic development, the embryonic disc becomes oval shaped, and then pear-shaped with the ...

. Implantation begins at about six days after fertilization, and lasts for about a week, during which time formation of the primitive streak occurs. 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.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). 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. 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. By this asexual reproduction, the parents of the original conceptus in effect become grandparents to the identical twin so conceived. In the United States, a report by the

National Institutes of Health The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the late ...

stated that a conceptus could be both a pre-implantation embryo and a pre-embryo at the same time. However,

Ann Kiessling Ann A. Kiessling is an American reproductive biologist and a researcher in human parthenogenic stem cell research at The Bedford Research Foundation. She was an associate professor in teaching hospitals of Harvard Medical School (Brigham and Wome ...

(a leader in stem cell research) has written that those categories are inaccurate.Kiessling, Ann
What is an Embryo?”
Connecticut Law Review 36 (4): 1051–93.

Ontological status

The illustration shows the ontological status of the preembryo,

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

, and

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...

: *(o) indicates the (natural &) standard reproductive and embryogenic pathway *(mz) indicates all the possible pathways for a monozygotic twin *(/c) indicates a clone created by either SCNT or ANT *(ch) indicates all the possible pathways for a chimeric individual *(dz) indicates the pathway of a

dizygotic twin Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of TwinLast Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two em ...

*(en) indicates an enucleated

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

*(m) indicates a hydatidiform mole *(cm) indicates a complete hydatidiform mole *(pm) indicates a partial hydatidiform mole, and *(p) indicates

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...

. *(O) indicates an

, *(Z) indicates a

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

, *(M) indicates a

morula A morula (Latin, ''morus'': mulberry) is an early-stage embryo consisting of a solid ball of cells called blastomeres, contained in mammals, and other animals within the zona pellucida shell. The blastomeres are the daughter cells of the zygote ...

, *(B) indicates a

blastocyst The blastocyst is a structure formed in the early embryonic development of mammals. It possesses an inner cell mass (ICM) also known as the ''embryoblast'' which subsequently forms the embryo, and an outer layer of trophoblast cells called the t ...

, *(E) indicates an

, *(F) indicates a

, *(I) indicates a live born individual person. *(PM) indicates a partial hydatidiform mole, *(CM) indicates a complete hydatidiform mole, *(T) indicates a

teratoma A teratoma is a tumor made up of several different types of tissue, such as hair, muscle, teeth, or bone. Teratomata typically form in the ovary, testicle, or coccyx. Symptoms Symptoms may be minimal if the tumor is small. A testicular terato ...

. The colors represent the maternal and paternal genetic contributions.

Footnotes

{{reflist Embryology

Pre-embryo in human embryonic development

Ontological status

See also

Footnotes