The following snip it is of a much longer article which grabbed my attention. Currently research is investigating the possibility of removing cells from an embryo and growing a twin from the cells. Researchers believe the high tech procedure will offer poor responders and older women with good quality embryos a larger pool of potential embryos for freezing and future transfer. Modern science is providing couples with a new tool to succeed in achieving pregnancy. It will be interesting to watch the outcome.
Volume 93, Issue 2, Pages 423-427 January 15, 2010
Human embryo twinning with applications in reproductive medicine
Karl Illmensee, Ph.D.ab, Mike Levanduski, M.S.ab, Andrea Vidali, M.D.a, Nabil Husami, M.D.a, Vasilios T. Goudas, M.D
Mammalian embryo splitting was first achieved in the mouse system by investigating the developmental potential of blastomeres isolated from early preimplantation embryos at the 4- and 8-cell stage. Further studies in the mouse showed that 65% of embryos split at the 2-cell stage and transferred to foster mothers developed to term. Moreover, transfer of embryos derived from 2-cell embryo splitting gave rise to healthy offspring very similar in size and morphology to control live-born mice originating from normal embryos. The investigators concluded that experimental embryo twinning did not interfere with normal adult development.
In farm animals, embryo splitting has successfully been established for several livestock species. In sheep, 36% of embryos split as 2- and 4- cell embryos developed to term after transfer to recipient females. In cattle, embryos split into individual blastomeres at the 4-cell stage could develop to term, giving rise to multiple monozygotic healthy calves. Bisected or biopsied early bovine embryos gave pregnancy rates similar to those obtained from intact control embryos. Thousands of twin calves resulting from embryo splitting have been born worldwide, and there have been no reports of abnormalities in the offspring due to the splitting procedure. Embryo twinning was therefore proposed for safe and efficient applications under commercial field conditions. Furthermore, cryopreserved split bovine embryos after their time-separated thawing and intrauterine transfer gave rise to healthy monozygotic calves of different ages. In the goat, monozygotic twin kids were produced from bisected early embryos. In addition, split embryos that were transferred to genetically identical females could develop to term in allogenic pregnancies, being genetically identical twins to these foster females (9). In the pig, split embryos were capable of full-term development giving rise to healthy twin piglets (10). In the horse, from split embryos created via blastomere biopsy at the 2- or 8-cell stage, healthy monozygotic foals were delivered at term pregnancy.
In nonhuman primates, however, embryo splitting has given only inferior results without leading to twin babies. The splitting of rhesus monkey embryos at the 8-cell stage resulted in one live-born monkey. Embryo twinning in the rhesus monkey has also been attempted by blastomere separation at the 2- and 4-cell stage and has led to two twin pregnancies but with no birth of monozygotic twins. Further investigations are needed to reveal the reasons for these limited results. Genetically identical rhesus monkeys would be very useful for the study of human-related twinning and tissue transplantation and may serve as a model system to investigate the epigenetic effects caused by the maternal environment during pregnancy.
Human embryo splitting carried out on genetically abnormal embryos has so far been presented only in a preliminary report. These embryos were obtained from IVF cycles and were donated for research. They were split at early cleavage stages, coated with artificial zona pellucida (ZP), and cultured in vitro. However, these split embryos were arrested in development after a few cell divisions at the most. In a commentary referring to these preliminary experiments and to embryo splitting in general, the merits of these attempts were acknowledged for future applications in reproductive medicine (16).
With regard to human embryo splitting, the Ethics Committee of the American Society for Reproductive Medicine (ASRM) considered favorably research on embryo splitting and stated in its report “since embryo splitting has the potential to improve the efficacy of IVF treatments for infertility, research to investigate the technique is ethically acceptable”. According to these recommendations, we have first established efficient blastomere biopsy for embryo splitting in the mouse as an experimental model system.
Our objectives for this current study were to apply the newly developed technology to human embryo splitting to evaluate its efficacy at different early embryonic stages (splitting efficiency) and to determine the best success rates of twin embryo development to the blastocyst stage under in vitro culture conditions (developmental efficiency).
Discussion
This study documented that it is possible to effectively split human embryos by blastomere biopsy. A significantly increased rate for embryo twinning was observed for the more advanced embryos split at the 6- to 8-cell stage than for those split at the 2- to 5-cell stage. When embryos were split at the 2- to 5-cell stage, it was not apparent which of those would have the potential to progress to the 6- to 8-cell stage or beyond. Of course, a similar argument could also be considered for the 6- to 8-cell embryos concerning their prospective developmental capacities. Further investigation is necessary to explain why embryo splitting at the 6- to 8-cell stage gave superior twinning results.
In general, split embryos hatched in advance of nonsplit embryos, suggesting an “assisted hatching effect.” This was facilitated by the ZP opening that was required for blastomere biopsy. It has been proposed that assisted embryo hatching may provide a beneficial effect for facilitating embryo implantation in patients with advanced age, with repeated implantation failures after several IVF or ICSI cycles, or with cryopreserved-thawed ET cycles.
Splitting of 6- to 8-cell embryos resulted in more developing embryos in comparison with the number of embryos available before splitting. The numerical increase of embryos obtained after splitting would have obvious clinical advantages for patients enrolled in IVF programs. Embryo splitting in ART may be applicable and considered for those patients termed as “low responders” with only a few oocytes retrieved after controlled ovarian stimulation. However, embryo splitting should only be considered if the embryos are of high quality and reach the 6- to 8-cell stage after IVF, as our study indicates. In this case, embryo splitting may increase the likelihood for obtaining a pregnancy since more embryos could be made available for intrauterine transfer. Embryo splitting would not be of practical benefit for patients with poor-quality embryos that do not develop to the 6- to 8-cell stage by day 3 postfertilization. Relevant to this crucial transition during early embryonic development, it was documented at the molecular level that maternally derived mRNA stored during oogenesis is used for protein synthesis from fertilization to the initial blastomere divisions. Thereafter, a new wave of embryonic mRNA is synthesized and is responsible for continuation of embryogenesis. From these data on gene-expression profiling of early embryos it seems reasonable to consider the 6-cell stage as most optimal for embryo twinning.
For couples with few embryos of good quality available during one IVF cycle, embryo splitting may yield additional embryos to be cryopreserved for subsequent transfer, potentially increasing the likelihood of a pregnancy and even providing time-separated twins. The Ethics Committee of the ASRM has stated in its report that “splitting one embryo into two or more embryos could serve the needs of infertile couples in several ways. As long as a couple is fully informed of the risk of such an outcome, there would appear to be no major ethical objection”. It has previously been postulated that embryo splitting at the blastocyst stage may be of benefit for patients with only one or few normal embryos obtained by IVF techniques. Indeed, duplication of embryos by microsurgical splitting to improve the chance of pregnancy should not cause a medical or ethical objection since monozygotic twins can occasionally occur in natural conception as well as in IVF cycles. Although there is a concern that embryo splitting may result in unequal cell distribution to the twin embryos, such distribution does not seem to interfere with normal development. There is evidence for the unequal allocation of cells to the twin embryos, leading to some genetic and phenotypic differences among healthy monozygotic twins.
In our present study, we have established efficient techniques for human embryo splitting to create developing twin embryos, although they originated from genetically abnormal (triploid) embryos. We are currently conducting a randomized controlled prospective study under Institutional Review Board approval to further corroborate and extend these findings. In the future it should be anticipated that such novel twinning technology will find clinical use in reproductive medicine.