Our experience highlights that methods for genotyping single blastomeres can be optimized for reliability and accuracy, but with multi-step technologies, are subject to chance error [19,36]. Chance extraneous contamination should be monitored through the inclusion of a polymor­phic marker multiplexed within the genotyping assay (presently being standardized in our laboratory). More than any other procedure in genetic diagnostics, PGD requires close collaboration with experts in reproductive medicine, and the success of assisted reproduction treat­ment is a factor limiting positive PGD outcome, with <25% of couples who initiate a cycle achieving an (unaf­fected) birth [37]. Thus, with present biomedical technolo­gies PGD continues to be a specialized procedure in pre­ventive genetics, alongside PND.