Deconstructing the myth of poor prognosis for fast-cleaving embryos on day 3. Is it time to change the consensus?
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To determine the developmental competence of fast-cleaving D3 embryos.
Retrospective study including 4028 embryos from 513 PGT-A cycles performed between July 2014 and June 2017. Embryos were cultured in time-lapse incubators and biopsied at blastocyst stage. Embryos were classified in groups according to the number of cells on D3 (from 2-cell to ≥13 -cell and compacted). A generalized linear mixed model adjusted for confounding factors was performed to assess the chance to give rise to an euploid blastocyst in each group compared with the chance of 8-cell embryos. Implantation and live birth rates were also analyzed.
The statistical analysis showed that embryos with 9 to 11 cells had a slightly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.77 (0.61–0.96)) while embryos with more than 11 cells were found to be just as likely to give rise to an euploid blastocyst as the 8-cell embryos (OR (95% CI) 1.20 (0.92–1.56)). Conversely, slow-cleaving embryos had a significantly lower euploid blastocyst rate than 8-cell embryos (OR (95% CI) 0.31 (0.24–0.39)). Moreover, euploid blastocysts derived from fast-cleaving embryos and from 8-cell embryos exhibit similar live birth rates. No significant differences were found in the chance to give rise a live birth between 8-cell and 9- to 11-cell embryos (OR (95% CI) 1.23 (0.70–2.15)) and > 11-cell embryos (OR (95% CI) 1.09 (0.57–2.09)).
Embryos with more than 11 cells exhibit similar developmental competence to 8-cell embryos. Their poor prognosis should be reconsidered.
KeywordsFast-cleaving embryos Cell number Blastocyst rate Euploidy rate Implantation rate Live birth rate
This work was performed under the auspices of “Càtedra d’Investigació en Obstetricia i Ginecologia” of Department of Obstetrics, Gynaecology and Reproductive Medicine; Hospital Universitari Dexeus, Universitat Autònoma de Barcelona.
M.C.P. and B.C. designed the study, interpreted the data, and wrote the manuscript. M.P., M.B., and A.V. edited and reviewed the manuscript. S.G. conducted the statistical analysis. I.G-F, B.C., and P.B. reviewed the manuscript. All authors approved the final version of the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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