Preimplantation genetic diagnosis.

Preimplantation genetic diagnosis (PGD) is the screening of embryos at the cleavage stage in order to select and transfer only the desired embryo. The main indications of PGD are monogenic disorders and aneuploidy. This article reviews the recent advances in PGD methodology and presents their advantages, disadvantages and challenges. Ethical considerations arising with more widespread use of PGD for physical traits is also discussed. PGD for monogenic disorders remains the most successful indication, but is technically more challenging. PGS for aneuploidy has passed through a period of reconsideration and is now re-emerging with complete genome screening.