Scientific references: cloning by "twinning" (embryo splitting", Jan. 2004)

Dianne Irving Comments
Dr. Dianne N. Irving, M.A., Ph.D.
copyright January 19, 2004
Reproduced with Permission

In perhaps an effort to panic the public into grudgingly agreeing to allow partial bans on human cloning to pass legislative bodies that supposedly (but don't) ban "reproductive" cloning but allow "therapeutic" (or "research") cloning, there has been a flood of articles in the last week expressing "outrage" over Dr. Zavos' recent claims in Great Britain that he has successfully implanted cloned embryos into women's uterus. But is the "outrage" really about violating women's rights by impregnating them with experimental cloned human embryos, or is it really a PR effort to rush defective legislation through?

For example, in just two of such articles of "outrage", one can easily pick out several of the PR subterfuges: [See, "Outrage at bid for first human clone", by Tom Curtis and Murdo MacLeod, Jan. 18, 2004 ( and, "It's morally repugnant for anyone to clone a human being", by Yakub Qureshi, Jan. 18, 2004 (, both in Scotland and Sunday]:

1. Panic people (especially women) into passing anything that might stop "reproductive" cloning but still allow "therapeutic" (research) cloning:

"It is morally repugnant that anyone would attempt to clone a human being. It is one thing to attempt to clone animals, but this is beyond the pale. We are meddling with human life and are on the edge of a huge moral abyss."

2. Assure them that, in Great Britain at least, such outrageous violations to women as "reproductive" cloning is fully addressed and forbidden by their 2001 House of Lords regulations (so they're safe);

"This government shares the widespread public repugnance that human cloning could be attempted. We made a manifesto commitment to prevent this happening in the UK and we acted swiftly to deliver this commitment by passing the Human Reproductive Cloning Act at the end of 2001. This explicitly bans any attempt to create a cloned human baby in the UK. We are also working to achieve a worldwide ban on reproductive cloning through the United Nations."

However, among the inherent problems with this British House of Lords bill are that the bill is based on the false scientific term "pre-embryo" (which has long been formally rejected by the International Nomina Embryologica Committee), and that it defines "human cloning" only in terms of one human cloning technique -- somatic cell nuclear transfer (SCNT). Thus British women are not protected by this bill against the implantation of human embryos that have been produced by means of the many other kinds of human cloning techniques. Even the article acknowledges that there are many kinds of human cloning techniques: "Cloning is an umbrella term used by scientists to describe a number of different processes for duplicating biological material." Nor, of course, are human embryos that are produced by these other cloning techniques regulated at all. [Please see my formal University Faculty For Life submission concerning this legislation to the House of Lords, complete with extensive and detailed scientific and philosophical references. For full text of the bill see; for acknowledgment of receipt of my UFL submission, see (acknowledgment); for URL of this UFL submission, see (full text)]

3. And, publicly, continuously ridicule Zavos' claims that he also plans to clone human twins by means of another (of many) cloning techniques called "embryo splitting" (people must not be allowed to think it is possible or they would have to regulate it too):

"Before announcing the implantation, Zavos had used the press conference to promote embryo splitting, the creation of two identical IVF twins of which one would be used as a source of spare body parts for the other. He said splitting could either be used to reproduce two embryos, or one could be kept back and frozen as an 'insurance policy' for the other embryo. ... Peter Braude, fertility expert at King’s College Hospital, said: 'The idea of splitting embryos is not new. It was done in animals 15 years ago. But it has always been accompanied by low success rates and has therefore never been accepted for us in humans. Zavos does not represent mainstream science and what he and his colleagues are doing is seeking publicity rather than advancing science.'"

The claims by Zavos that he could next clone human twins by means of one of those other cloning techniques, embryo splitting, has been documented in human embryology texts, as well as hailed and promoted by IVF centers in their literature and on their websites for many years now. [See direct quotations from many such references below].

Hmmmmmmmmm. British women should worry.

Scientific references for cloning by means of "embryo splitting", "blasomere separation", "embryo multiplication", "twinning":

Many IVF providers are strongly promoting the use of twinning cloning techniques, a process they refer to as "embryo multiplication", e.g.: "Because early embryonic cells are totipotent, the possibility of splitting or separating the blastomeres of early preimplantation embryos to increase the number of embryos that are available for IVF treatment of infertility is being discussed Because embryo splitting could lead to two or more embryos with the same genome, the term "cloning" has been used to describe this practice. ... Whereas these ethical concerns raise important issues, neither alone nor together do they offer sufficient reasons for not proceeding with research into embryo splitting and blastomere separation. ... In sum, since embryo splitting has the potential to improve the efficacy of IVF treatments for infertility, research to investigate the technique is ethically acceptable. Persons asked to donate gametes or embryos for such research should be fully informed that research in embryo splitting is intended or planned as a result of their donation. The fears of possible future abuses of the technique are not sufficient to stop valid research in use of embryo splitting as a treatment for infertility. This statement was developed by the American Society for Reproductive Medicine's Ethics Committee and accepted by the Board of Directors on December 8, 1995." See, AMERICAN SOCIETY OF REPRODUCTIVE MEDICINE, at:

See also: "New Ways to Produce Identical Twins -- A Continuing Controversy": "Now, a new method of actually producing identical twins looms near. Called "blastomere separation" (the separation of a two- to eight-cell blastomere into two identical demi-embryos), it is potentially one method of helping infertile couples have children through in vitro fertilization (IVF). ... The following is excerpted from the medical journal Assisted Reproduction Reviews, May 1994. Dr. Joe B. Massey, who heads an in vitro clinic in Atlanta. Dr. Massey reviews the advances in blastomere separation and discusses the potential indications, benefits, limitations, and ethics of using this method to produce monozygotic twin embryos for IVF patients. The Twins Foundation, by presenting Dr. Massey's material for your information neither advocates nor rejects any such procedures: 'Embryo Multiplication by Blastomere Separation -- One Doctor's Proposal’. [Massey]: In spite of many advances in human in vitro fertilization (IVF), there are still many problems. ... According to Dr. Massey, 'Observations on the potential impact of removing less than half of the cells from the human embryo have been well documented in pre-clinical embryo biopsy studies.' (For more on this story see Research Update Vol. 9, No. 1, 1994)." See, THE TWINS FOUNDATION, at:

See also: Professor Dr. Mithhat Erenus, "Embryo Multiplication": "In such cases, patients may benefit from embryo multiplication, as discussed in the study by Massey and co-workers. ... Since each early embryonic cell is totipotent (i.e., has the ability to develop and produce a normal adult), embryo multiplication is technically possible. ... In humans, removal of less than half of the cells from an embryo have been documented. No adverse effects were reported when an eighth to a quarter of the blastomeres were removed from an embryo on day 3 after insemination. ... Further evidence supporting the viability and growth of partial human embryos is provided by cryopreservation. After thawing four-cell embryos, some cells may not survive, leaving one-, two-, or three-cell embryos. These partial embryos survive and go to term, but at a lower rate than whole embryos. ... Based on the results observed in lower order mammals, the critical period of development to ensure success in separating human blastomeres should be at the time of embryonic gene expression, which is reported in humans to be between the four- and eight-cell stages [twinning by "blastomere splitting"]. .... The second potential method of embryo multiplication is blastocyst splitting. ... For couples who have less than three quality embryos for transfer, blastomere separation could be of benefit.." at:

See also "embryo self-selection": "The ability to grow embryos for five days to the blastocyst stage of development in the laboratory, rather than the traditional three days, allows clinicians to determine with greater certainty which embryos are really the "best" in terms of their potential for implantation. Consequently, blastocyst culture makes it possible to select the best one or two blastocysts vs. three or four early embryos to transfer back to the mother. Fertility centers like Shady Grove constantly strive to improve IVF success rates through the steady refinements of clinical and laboratory techniques. Clinical blastocyst culture and transfer is the next important step in that evolution,' explains Robert Stillman, MD: 'After five days of growth, the cells of the embryo should have divided many times over, and have begun to differentiate by function. The embryos that survive to this stage of development are usually strong, healthy, and robust. ... Simply put, this self selection can be viewed as 'survival of the fittest. ... Which ones to transfer? Which ones are really the "best'? Two additional days in the blastocyst culture medium allows the natural winnowing process to continue. Thus, after 5 days of growth in the laboratory, only 2 or 3 of the original ten embryos may remain viable. We now know the best embryos to transfer. ... In thinking of the example above, patients who have fewer oocytes retrieved, fewer fertilized or fewer dividing embryos by day three in culture have no advantage using blastocyst culture, since little is to be gained in further embryo 'self selection'. Dr. Stillman emphasizes."


Also, ETHICS COMMITTEE OF THE AMERICAN SOCIETY FOR REPRODUCTIVE MEDICINE, "'Ethical Considerations of Assisted Reproductive Technologies': Originally published as a supplement to the ASRM medical journal (Fertility and Sterility 1994;62:Suppl 1), Ethical Considerations for Assisted Reproductive Technologies covers the American Society for Reproductive Medicine's position on several aspects of reproductive medicine, including: ... the moral and legal status of the preembryo, ... the use of donor sperm, donor oocytes and donor preembryos, ... the cryopreservation of oocytes and preembryos, micro techniques such as: zona drilling, microinjection, blastomere separation (cloning), and assisted hatching." at:

Such types of cloning is also fully acknowledged in human embryology and human molecular textbooks:

"The embryo enters the uterine cavity after about half a week ... Each cell (blastomere) is considered to be still totipotent (capable, on isolation, of forming a complete embryo), and separation of these early cells is believed to account for one-third of cases of monozygotic twinning." (p. 37) "... Biopsy of an embryo can be performed by removing one cell from a 4-cell, or two cells from an 8-cell, embryo. This does not seem to decrease the developmental capacity of the remaining cells." [O'Rahilly and Muller 2001, p.37]

"Of the experimental techniques used to demonstrate regulative properties of early embryos, the simplest is to separate the blastomeres of early cleavage-stage embryos and determine whether each one can give rise to an entire embryo. This method has been used to demonstrate that single blastomeres, from two- and sometimes four-cell embryos can form normal embryos, ... " (p. 44); " ... Some types of twinning represent a natural experiment that demonstrates the highly regulative nature of early human embryos, ..." (p. 48); "... Monozygotic twins and some triplets, on the other hand, are the product of one fertilized egg. They arise by the subdivision and splitting of a single embryo. Although monozygotic twins could ... arise by the splitting of a two-cell embryo, it is commonly accepted that most arise by the subdivision of the inner cell mass in a blastocyst. Because the majority of monozygotic twins are perfectly normal, the early human embryo can obviously be subdivided and each component regulated to form a normal embryo." (p. 49) [Carlson 1999]

"If the splitting occurred during cleavage -- for example, if the two blastomeres produced by the first cleavage division become separated -- the monozygotic twin blastomeres will implant separately, like dizygotic twin blastomeres, and will not share fetal membranes. Alternatively, if the twins are formed by splitting of the inner cell mass within the blastocyst, they will occupy the same chorion but will be enclosed by separate amnions and will use separate placentae, each placenta developing around the connecting stalk of its respective embryo. Finally, if the twins are formed by splitting of a bilaminar germ disc, they will occupy the same amnion." (p. 325) [Larsen 1998]

"Another means of demonstrating the regulative properties of early mammalian embryos is to dissociate mouse embryos into separate blastomeres and then to combine the blastomeres of two or three embryos. The combined blastomeres soon aggregate and reorganize to become a single large embryo, which then goes on to become a normal-appearing tetraparental or hexaparental mouse. By various techniques of making chimeric embryos, it is even possible to combine blastomeres to produce interspecies chimeras (e.g., a sheep-goat)." (p. 45); "... The relationship between the position of the blastomeres and their ultimate developmental fate was incorporated into the inside-outside hypothesis. The outer blastomeres ultimately differentiate into the trophoblast, whereas the inner blastomeres form the inner cell mass, from which the body of the embryo arises. Although this hypothesis has been supported by a variety of experiments, the mechanisms by which the blastomeres recognize their positions and then differentiate accordingly have remained elusive and are still little understood. If marked blastomeres from disaggregated embryos are placed on the outside of another early embryo, they typically contribute to the formation of the trophoblast. Conversely, if the same marked cells are introduced into the interior of the host embryo, they participate in formation of the inner cell mass. Outer cells in the early mammalian embryo are linked by tight and gap junctions ... Experiments of this type demonstrate that the developmental potential or potency (the types of cells that a precursor cell can form) of many cells is greater than their normal developmental fate (the types of cells that a precursor cell normally forms)." (p. 45); " ... Classic strategies for investigating developmental properties of embryos are (1) removing a part and determining the way the remainder of the embryo compensates for the loss (such experiments are called deletion experiments) and (2) adding a part and determining the way the embryo integrates the added material into its overall body plan (such experiments are called addition experiments). Although some deletion experiments have been done, the strategy of addition experiments has proved to be most fruitful in elucidating mechanisms controlling mammalian embryogenesis." (p. 46). [Carlson 1999]

National Institutes of Health, Office of Science Planning and Policy, "CLONING: Present Uses and Promises", April 27, 1998), at: "Cloning and somatic cell nuclear transfer are not synonymous. Cloning is the production of a precise genetic copy of DNA, a cell, or an individual plant or animal. Cloning can be successfully accomplished by using a number of different technologies. Somatic cell nuclear transfer is one specific technology that can be used for cloning." See also: Australia, The Cloning of Humans (Prevention) Bill 2001 (Queensland): "Cloning can occur naturally in the asexual reproduction of plants, the formation of identical twins and the multiplication of cells in the natural process of repair. The cloning of DNA, cells, tissues, organs and whole individuals is also achievable with artificial technologies. ... The cloning of a cell or an individual may be achieved through a number of techniques, including: molecular cloning ..., blastomere separation (sometimes called "twinning" after the naturally occurring process that creates identical twins): splitting a developing embryo soon after fertilisation of the egg by a sperm (sexual reproduction) to give rise to two or more embryos. The resulting organisms are identical twins (clones) containing DNA from both the mother and the father. ... somatic cell nuclear transfer: the transfer of the nucleus of a somatic cell into an unfertilised egg whose nucleus, and thus its genetic material, has been removed. A number of scientific review bodies have noted that the term "cloning" is applicable in various contexts, as a result of the development of a range of cloning techniques with varying applications", at: