Preimplantation genetic diagnosis (PGD) allows embryos created through in vitro fertilization to be tested for genetic defects before implantation. It is primarily used for two groups - individuals at high risk of passing on genetic diseases to prevent disease or termination of pregnancies, and to screen embryos for chromosomal abnormalities to improve IVF success rates. The techniques used include biopsy of polar bodies or blastomeres from embryos, followed by analysis using polymerase chain reaction, fluorescence in situ hybridization, or comparative genomic hybridization. PGD is most commonly used for common single gene disorders and chromosomal translocations but is limited by the technical challenges of testing single cells.