Preimplantation diagnosis of inherited and chromosomal diseases allows couples at risk of conceiving a genetically abnormal fetus to avoid the birth of an affected child without the need for a prenatal diagnosis and selective abortion of an affected fetus. For some couples this may be the only option, because they cannot accept termination of pregnancy as a measure of avoiding the birth of an affected child. Even for those who accept prenatal diagnosis, repeated termination of pregnancy forces them to look for other options to control the outcome of their pregnancies from the very outset. This may be achieved by genetic analysis of oocytes or cleaving embryos, which opens a new prospect for ‘prepregnancy’ genetic diagnosis. As will be shown, such an approach will also be a useful addition to assisted reproduction technologies, at least for in vitro fertilization (IVF) patients of advanced maternal age.