Fast-cleaving embryos on Day 3 are as viable as the eight-cell embryos considered to have a better prognosis
According to the results of various studies and data agreed among experts of the Spanish Association for the Study of Reproductive Biology (ASEBIR) and the Embryology Special Interest Group of the European Society of Human Reproduction (ESHRE), eight-cell embryos on Day 3 are considered to have a better prognosis than those with more than eight cells, which are faster growing, both as regards their viability in pre-implantation diagnosis (PGD) tests and in uterine implantation and pregnancy rates.
However, a group of investigators from the Reproductive Medicine Unit of Dexeus Mujer, led by embryologist Carme Pons, conducted a retrospective observational study on a sample of 4,028 embryos obtained between July 2014 and June 2017, classified into groups by their rate of growth on day 3 of their development. Of the total embryos, 1,216 (30.2%) had less than 8 cells (slow-cleaving embryos), 1,358 (33.7%) had eight cells, and 1,454 (36.1%) had more than eight cells (fast-cleaving embryos).
After genetic testing (PGD), the team found that 20.6% of fast-cleaving embryos were diagnosed as chromosomally normal (euploid), a very similar figure to the 22.7% for eight-cell embryos. By contrast, this percentage dropped to 8.7% in slow-cleaving embryos. The uterine implantation rate was actually higher among fast-cleaving embryos: 67.5% compared to the 57.8% of eight-cell embryos, which are considered ideal. The rate among slow-cleaving embryos was lower at 43.7%. This led the authors to conclude that fast-cleaving embryos on Day 3 have the same probabilities of developing into blastocysts, being chromosomally normal and of implanting as eight-cell embryos.
Deconstructing the myth of poor prognosis for fast-cleaving embryos on Day 3. Is it time to change the consensus?
M.C. Pons, B. Carrasco, M. Parriego, B. Coroleu, P. N. Barri, M. Boada, A. Veiga.
Department of Obstetrics, Gynaecology and Reproduction. Hospital Universitari Dexeus, Barcelona.
ESHRE 2018 oral communication