Out of the 126 embryos, 62 (49.2%) were euploid and 64 (50.8%) were aneuploid at day three; of these 43 (69.4%) of the euploid embryos developed to the blastocyst stage, while only 25 (39.1%) of the aneuploid embryos did. Of the 25 aneuploid day-five embryos, 68% possessed a euploid ICM and 76% possessed a euploid TE, with 64% having both a euploid ICM and TE. Therefore, 16 of the 25 had correction in both the TE and ICM cells.
Prof Kearns said: "These results suggest that there is a dynamic process of genetic normalisation that occurs in the developing human embryo. It is likely that there is considerable cellular mosaicism in many cleavage stage embryos and that there are mechanisms in place that cause marginalisation of abnormal cells while allowing growth of normal cells. The exact mechanisms that allow this, however, at this time are still unknown. The existence of such a process has significant implications for furthering numerous scientific fields."
For fertility treatment, the discovery that a large percentage of embryos deemed to be abnormal at day three could become normal at day five suggests that during PGS, day five is the better time to predict the ultimate chromosomal status of the embryo, rather than day three. In addition, if a day-three embryo was found to be aneuploid, then these findings suggest that it would be worth waiting and testing the trophectoderm at day five before making the
|Contact: Hanna Hanssen|
European Society of Human Reproduction and Embryology