Preimplantation genetic diagnosis and embryo research--human developmental biology in clinical practice.

Research on human preimplantation embryos in vitro is controversial. Yet it has been the cornerstone for the development important clinical assisted conception techniques. Preimplantation genetic diagnosis which has developed out of this assisted reproductive technology for the first time provides a realistic alternative to prenatal diagnosis and abortion for couples who are at substantial risk of conceiving a pregnancy affected by a known genetic disorder. It also provides the first real hope of therapy for couples who have suffered repeated miscarriages due to chromosome translocations. However, the ability to test very early embryos in vitro presents new and unusual ethical challenges for clinicians and developmental biologists.