Preimplantation genetic screening (PGS) checks the chromosomes of embryos conceived through IVF to select normal embryos for implantation. PGS may be recommended for women over 35 due to increased risk of chromosome abnormalities with age, those with a genetic history of disorders, repetitive miscarriages, or recurrent implantation failure where fertilized eggs fail to implant. PGS can help identify chromosome issues that may lead to conditions like Down syndrome and help improve chances of pregnancy success.