Preimplantation genetic screening: after 25 years and a complete make-over, the truth is still out there
More than 25 years ago, it was found that human embryos of about three days old cultured in the lab, showed chromosomal abnormalities in more than half of them. Many of these abnormalities were not coming from the sperm or the egg, but occurred after the embryo has cleaved two times, obtaining four cells, or three times, reaching the eight-cell stage.