Abstract: With the application and improvement of preimplantation genetic test (PGT), the detection rate of mosaic embryos in preimplantation embryos， as the third embryo type other than euploid embryos and aneuploid embryos，is increased. Embryonic mosaicism can increase the risk of miscarriages，stillbirths and genetic abnormalities. However, some mosaic embryos can also result in healthy-live births. Mosaic embryos differ in the types of chromosomal abnormalities, the proportion of abnormal cells and the mosaic sites, which makes great challenge for the choice of transplantation and the uncertainty of clinical outcomes. Meiotic mistakes in gametogenesis lead to aneuploid embryos; mitotic errors during post-zygotic cell division contribute to mosaic embryos. It is very important to understand the mechanism of embryonic mosaicism, incidence, influencing factors and clinical outcomes, for us to avoid falsely discarding embryos with developmental potential.

Key words: Mosaicism, Chromosomes, Aneuploidy, Embryo implantation, Preimplantation diagnosis