Embryo Selection: Past, Present, and Future
10 February 2014 (online)
Although most clinicians would agree that a singleton live birth is the best possible outcome from in vitro fertilization (IVF), transfer of multiple embryos has been the norm because it has not been possible to determine which, if any, embryos within a cohort are capable of developing into a healthy baby. In the early years of IVF, physicians frequently transferred high numbers of embryos in an attempt to achieve acceptable success rates. Cryopreservation was an option for embryos not selected for embryo transfer, but the success rates of frozen embryo transfer were initially not high, and focus was placed on achieving a live birth from the fresh embryo transfer. It was soon realized that transfer of multiple embryos could lead to twins, triplets, and even higher order multiple gestations. Multiple pregnancies are associated with increased risk for maternal obstetric complications and many serious consequences of infant prematurity. Thus, techniques such as extended embryo culture were developed to improve the ability of embryologists to choose a limited number of embryos for transfer.
In the last decade, multiple approaches have been developed with the goal of improving the process of embryo selection. Some of these techniques have proven fruitful, whereas others have not demonstrated clear benefit. In addition, some techniques are in development and show promise, but they still need to be proven effective and be available at affordable cost before widespread use. Physicians and embryologists are in need of accurate information which describes these advances to help them to determine if and how to incorporate available technologies within their practice.
This issue of Seminars in Reproductive Medicine provides a comprehensive review of the state of the art and potential future for techniques of embryo selection. As the authors describe, the technologies available for genetic analysis of embryos has greatly increased the accuracy of preimplantation genetic screening for aneuploidy and has expanded the potential of preimplantation diagnosis for single gene disorders. Embryo morphology remains an important element of embryo selection. Advances in our understanding of early embryo development have led to the possibility of using time-lapse imaging or metabolomics to aid in embryo selection. An alternative to advanced techniques of embryo selection, cryopreservation and serial elective single embryo transfer, is also presented.
The percentage of cycles with elective single embryo transfer has increased over time. According to the data reported to the Society for Assisted Reproductive Technology, elective single embryo transfer was used in 11.7% of fresh autologous IVF cycles for women younger than 35 years of age in 2011, and with improved methods of embryo selection, it is hopeful that this trend of increasing utilization of elective single embryo transfer will continue. Although the techniques for embryo selection have improved significantly over the last decade, further refinements are needed and some technologies are not yet available in all centers. The cost-effectiveness and safety of newer technologies need further study to help clinicians to know when particular methods are best employed. Despite these limitations, the authors in this issue point out that we have come a long way toward being able to distinguish viable from nonviable embryos. With continued advances, there is hope that we will, at some point in the not-to-distant future, be able to maximize the chance of a singleton healthy live birth with very minimal risk of multiple gestations.
- 1 Society for Assisted Technology National Data Summary. https://www.sartcorsonline.com/rptCSR_PublicMultYear.aspx?ClinicPKID=0 . Accessed October 6, 2013