UK researchers using light‑sheet microscopy published long‑duration live imaging of late‑stage human preimplantation embryos and observed de novo chromosome segregation errors in trophectoderm cells. The Nature Biotechnology papers document mitotic errors that can arise after the developmental window when preimplantation genetic testing for aneuploidy (PGT‑A) is typically performed, raising concerns that PGT‑A may overcall embryo abnormality. The teams combined fluorescent nuclear tagging, electroporation of tagged mRNA, and deep‑learning segmentation to track divisions in 3D, offering direct evidence that aneuploidies can emerge during blastocyst stage development.