Abstract: PGS， as a technique of early prenatal diagnosis， has been performed in resent years as a way of improving pregnancy and live birth rates for patients. PGS identifies chromosomal abnormalities in embryos before transferred. After PGS， embryos with normal number of chromosomes are selected to transfer to the uterus. It is a kind of PGD with low risk. ESHRE PGD Consortium reported that the cycles of PGS account for more than half of the PGD cycles， and this proportion of PGS is increasing year by year. It has been performed in patients with advanced maternal age， recurrent implantation failure， recurrent miscarriage， and so on， for acceptable pregnancy rates. Although PGS offered a way for those patients with some risk factors， its effectiveness remains acataleptic at present. In this review， application of PGS and problems in diagnosis of early human embryos were discussed.

Key words: Preimplantation diagnosis, Genetic screening, In situ hybridization, fluorescence, Aneuploidy, Mosaic chimera