To the Editor:
In a recent study (1), an important question has been mooted, namely, “Should we assess early cleavage between 25 to 27 hours after insemination, with the aim of yielding any benefit in the clinical outcomes?” The message I have been delivered by the results has been, “There was not any benefit of early cleavage assessment, unless all transfer embryos were of sub-optimal quality.” Promoted by ASEBIR with a clear aim to conclude with a scientifically based recommendation to embryologists, I think the results need to be evaluated under scrutiny.
I believe the study missed the important point of what to look for between 25 to 27 hours after insemination. It is difficult to justify the exception of early-cleaved zygotes, while morphologic variations among embryos (and gametes) are well recognized among professionals. As for gametes and embryos, significant biological events and molecular/metabolic activities take place during the zygotic cell cycle (2) with an impact reflected by morphology (3). However, observations within this particular developmental period have a tendency to limit themselves merely to the time of the event. They sometimes exclude how the event has been exhibited, which contradicts the basic concepts of science in developmental biology and perhaps causes variations in results.
As cited by the authors, our group has brought to light the impact of early cleavage morphology on clinical outcomes and results subsequently confirmed (4, 5). These papers agreed that even early cleavage (two-cell embryos displaying less than 20% difference in blastomere volume and less than 20% fragmentation) was superior in clinical outcomes to other division patterns. Given similarity to cleavage stage embryos, this was not a surprise.
It is inevitable that the comprehensive morphological description, “cleavage to two or more blastomeres,” as in the current study will fail to show any clinical benefit. Although the authors accurately state the compromised outcome of embryos exhibiting direct or rapid cleavage and the (insignificant) difference in the implantation rates for multinucleated from non-multinucleated two-cell embryos (24.2% versus 36.5%, respectively), they don’t take into account other cleavage patterns and nuclear morphologies (with or without fragmentation) and fail to give a more robust definition of early cleavage.
Furthermore, the findings obtained from time-lapse technology do not contradict nor decrease the value of early cleavage assessments, but support and strengthen them with strong scientific verification (some given above). As accurately proven earlier by dynamic monitoring studies, “Timing is everything in the human embryo,” and approaches to the duration of first cytokinesis (indirectly referring to overall duration of the first cell cycle) should be from the “morphokinetic” perspective, despite being a predictive factor for blastocyst formation.
An accurate interpretation of the value of early cleavage assessment requires similar attention to the material observed during this particular time frame of development as their predecessors and successors. The authors may like to re-evaluate their data after such considerations.
H. Nadir Ciray, M.D., Ph.D.
Division of Reproduction and Early Development, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds, United Kingdom.
1. de los Santos M, Arroyo G, Busquet A,Calderon G, Cuadros J, Victoria M, et al. A multicenter prospective study to assess the effect of early cleavage on embryo quality, implantation, and live-birth rate. Fertil Steril 2014.
2. Ramos L, de Boer P. The role of the oocyte in remodelling of the male chromatin and DNA repair: Are events in the zygotic cell cycle of relevance to ART? Biennial Review of Infertility 2011;2:227-43.
3. Somfai T, Inaba Y, Aikawa Y, Ohtake M, Kobayashi S, Konishi K, et al. Relationship between the length of cell cycles, cleavage pattern and developmental competence in bovine embryos generated by in vitro fertilization or parthenogenesis. The Journal of Reproduction and Development 2010;56:200-7.
4. Hesters L, Prisant N, Fanchin R, Mendez Lozano DH, Feyereisen E, Frydman R, et al. Impact of early cleaved zygote morphology on embryo development and in vitro fertilization-embryo transfer outcome: a prospective study. Fertil Steril 2008;89:1677-84.
5. Terriou P, Giorgetti C, Hans E, Salzmann J, Charles O, Cignetti L, et al. Relationship between even early cleavage and day 2 embryo score and assessment of their predictive value for pregnancy. Reproductive Biomedicine Online 2007;14:294-9.
Published online in Fertility and Sterility doi: 10.1016/j.fertnstert.2014.02.051
The authors respond:
Despite the promise of the “omic” approach in embryo selection, its actual use on a daily basis is still impending. Therefore, we embryologists need to rely on other non-invasive alternatives mainly focused on embryo morphology, which is the unique, tangible, and non-invasive tool for selecting embryos in IVF, and the search for new phenotypes that help select the best embryos for transfer. More than 10 years ago, EC was considered to be the warrant of promising phenotypes associated with both embryo quality and live birth (1), but it required performing additional embryo assessments at the time that the first mitotic division was expected to occur, requiring additional removals of the embryos for the incubators at a delicate time of the cellular cycle comprising G2 and mitosis phases.
Early cleavage has been associated with embryo quality and implantation rates; however, the benefit of checking for EC is not sufficiently clear. As a matter of fact, the Istanbul consensus group leaves to the laboratory the decision of whether or not to include the EC variable in embryo selection (2).
In our prospective multicenter study, we saw that selecting embryos by morphology (number of blastomeres, symmetry, fragmentation, multinucleation, etc.) on day 2 or day 3 is actually a better model for implantation than EC. Most of the embryos that undergo mitosis at 25-27 hours post-insemination are actually embryos with a good morphology on day 2 or day 3, in both egg donation cycles and in cases with own oocytes. Therefore, observing early cleavage does not add any benefit at all and actually may add more laboratory workload and more distortion to the embryo culture conditions.
Regarding the era of time-lapse technology, where it is easier to combine enormous variety of morphological assessments with specific kinetic parameters throughout the entire embryo development, revisiting an old parameter as EC may be meaningless. Time-lapse technology gives us a universe of information to explore and the possibility to build new algorithms without disturbing embryo culture conditions. Interestingly though, many of the algorithms do not find EC as a strong predicting embryo phenotype for implantation, which agrees with the perspective we defend in this letter (3).
When the time comes that this technology is accessible to all IVF laboratories, this suggestion could be helpful and should be taken into account.
In response to the question of whether EC should be assessed in routine practice, I would say that there is no need to do the same job twice. Looking at day 3 embryo morphology will be sufficient for selecting embryos for cleavage stage embryo transfers.
Maria José de los Santos, Ph.D.
IVF Laboratory, IVI Valencia, Valencia, Spain
1. Lundin K, Bergh C, Hardarson T. Early embryo cleavage is a strong indicator of embryo quality in human IVF. Hum Reprod. 2001;16(12):2652-7.
2. The Istanbul consensus workshop on embryo assessment: proceedings of an expert meeting. Hum Reprod. 2011;26(6):1270-83.
3. Meseguer M, Herrero J, Tejera A, Hilligsoe KM, Ramsing NB, Remohi J. The use of morphokinetics as a predictor of embryo implantation. Hum Reprod. 2011;26(10):2658-71.
Published online in Fertility and Sterility doi: 10.1016/j.fertnstert.2014.02.053