title: A zygote is not an embryo: ethical and legal considerations.
abstract: In spite of several past attempts at defining the point at which conception can be considered completed, resulting in the formation of an embryo, the existing definitions are still contradictory. In the absence of clear terminology, the application of laws aimed at the protection of early human life may have inadequate consequences for the efficacy of the current techniques of human infertility treatment. In this paper biological arguments are revisited, suggesting that the only point at which a clear demarcation line between what is and what is still not an embryo can be drawn is the moment of nuclear syngamy at the outset of the first cleavage division. The term 'zygote' is suggested to denote entities composed of spermatozoon and oocyte components before nuclear syngamy. It is suggested that the current embryo protection laws should not concern the zygote stage: at this stage, the main features that are said, in documents issued by different ethical and legal authorities, to characterize the early human embryo, namely the inseparable union of the male and female contribution, cell division and an autonomous control over cell division, are still not present. This reasoning strictly applies to embryos of biparental (paternal and maternal contribution) origin and cannot be extrapolated to embryos created by cell nuclear transfer (cloning). The application of embryo protection laws from the nuclear syngamy stage onwards can regulate embryo and embryo-derived stem cell research while still preserving the current high standard and efficacy of infertility treatment, which is of immediate interest to millions of infertile couples throughout the world.
authors.affiliation: MAR& Gen, Molecular Assisted Reproduction and Genetics, Gracia 36, 18002 Granada, Spain. cmendoza@ugr.es
authors.forename: Jan
authors.initials: J
authors.lastname: Tesarik
authors.forename: Ermanno
authors.initials: E
authors.lastname: Greco
mesh_terms: D001755:Blastocyst; D033041:Embryo Research / Q000941:ethics* / Q000331:legislation & jurisprudence; D004622:Embryo, Mammalian; D004992:Ethics, Medical; D005307:Fertilization in Vitro / Q000941:ethics* / Q000331:legislation & jurisprudence; D005858:Germany; D006801:Humans; D007246:Infertility / Q000628:therapy; D013030:Spain; D015053:Zygote