The investigators previously developed approaches to SNP-, CNV- and haplo-type single human cells (Vanneste et al. 2009, Nature Medicine). These methods open the possibility to be developed into a novel generic diagnostic technique which broadens the spectrum of disease-alleles that can be selected against during preimplantation genetic diagnosis (PGD) and which enables to help those couples that cannot be supported by PGD yet. PGD is the genetic analysis of a single blastomere from an in vitro fertilized (IVF) embryo and it is offered to couples to avoid the transmission of heritable genetic disorders to their offspring. PGD analyses are performed for (1) autosomal dominant or recessive monogenic diseases, (2) X-linked disorders and (3) chromosomal aberrations that may result in aneuploid conceptions. This novel method is likely to outperform and hence, replace current techniques for preimplantation genetic diagnosis. In this project the investigators will bring the technology from a proof-of-principle to the clinical application. To this end the investigators will make computational improvements for accurate single blastomere SNP-, CNV- and haplo-typing and perform a large validation study. For the validation studythe investigators will analyse the genomes of the blastomeres derived from 60 spare embryos of different origin: (1) Embryos diagnosed as genetically abnormal using current PCR- and FISH-protocols. (2) Embryos diagnosed as normal for the investigated region using current PCR- and FISH-protocols, but not of sufficient quality to be transferred or frozen. (3) Embryos of the sex that is selected against following PGD based sex-selection, or embryos of the sex that is selected for but of insufficient quality to be transferred or frozen. (4) Embryos that were not biopsied in a PGD cycle since they suffer a slight growth delay. This validation study will allow us to evaluate (1) the clinical validity (false positive and negative rate) and (2) clinical applicability (in terms of ease of use, success rate, etc.). In addition, it will bring us essential further fundamental insights in the origins and mechanisms of chromosomal instability operating during early embryogenesis and its consequences for clinical applications of PGD. Finally, following the validation study, this project will clinically implement the technique to treat 10 families.