title: Guest editorial.
authors.affiliation: UCL Centre for Preimplantation Genetic Diagnosis, Department of Obstetrics and Gynaecology, University College London, 86-96 Chenies Mews, London, WC1E 6HX, U.K.
authors.initials: JC
authors.lastname: Harper
authors.initials: E
authors.lastname: Pergament
authors.initials: JD
authors.lastname: Delhanty