FISH scoring criteria The specific FISH signals detected in a given blastomere were interpreted as follows: (i) a blastomere was considered to be diploid when the two gonosomes and two chromosome 13-, 16-, 18-, 21- and 22 specific signals were present; (ii) a blastomere was considered to be haploid, triploid or tetraploid when respectively one, three or four signals for the investigated chromosomes were present; (iii) a blastomere was considered to be aneuploid when an extra (trisomic) or missing (monosomic) signal for one chromosome was observed, in the presence of two signals for the remaining chromosomes analysed; (iv) a blastomere was considered as combined abnormal when it was neither diploid nor haploid, triploid, tetraploid or aneuploid. After FISH analysis, only embryos found to be chromosomally normal in the corresponding biopsied blastomere were transferred on day 5. FISH analysis was performed by experienced cytogeneticists trained in cytogenetics and FISH analysis. The results of the first and second round were analysed by two observers using a Zeiss Axioplan 2 fluorescence microscope.