Preimplantation genetic diagnosis (PGD) is a complex process comprising many stages and involving a multidisciplinary team of healthcare professionals. PGD allows a couple to conceive pregnancy that is biologically their own and is unaffected by the genetic condition in the family. Embryos are created by using assisted reproductive technology (ART) and are tested for the relevant genetic condition by polar body, blastomere or trophectoderm biopsy. It is important to distinguish the difference between PGD and preimplantation genetic screening (PGS) for sporadic chromosome aneuploidy. PGS is distinct from PGD and it is mainly used within the ART arena as an adjunct to fertility treatment with the aim of improving in vitro fertilisation (IVF) outcome. The potential use of PGD to select embryos with desirable nonmedical traits such as intelligence, beauty or longevity perhaps represents a more distant future for PGD.

This chapter deals with the issues that are discussed at an initial preimplantation genetic diagnosis (PGD) consultation, and describes the relevance and benefits of genetic counseling at this stage in the referral process. Chromosomal rearrangements initially believed to carry reproductive risk in the form of miscarriage or physical or mental disability, where family members may have considered prenatal testing, may be reevaluated and thus now represent normal variants without reproductive risk. The reproductive options for couples at risk of genetic disease will usually have been addressed by the genetic clinician prior to the referral for PGD. For many patients the time between taking a positive pregnancy test and undertaking prenatal diagnosis (PND) is a huge emotional burden that they know may end unsuccessfully. Many centers offering PGD are now able to do so for genetic disorders that may not affect an individual until adulthood, for example Huntington disease.