The objective of this study was twofold; first we wanted to determine the number of blastocysts needed at a certain age to produce at least one euploid blastocyst (>95%) through PGS using whole comprehensive chromosome screening. Secondly, we evaluated the chance of obtaining a euploid embryo in the next cycle after obtaining all aneuploid embryos. DESIGN: Retrospective cohort study. MATERIALS AND METHODS: 10,852 cycles of PGS were performed using blastocyst biopsy and analyzed by array Comparative Genomic Hybridization (aCGH). A total of 58,798 embryos were analyzed. IVF cycles were performed at multiple fertility centers and biopsies sent to a reference laboratory for analysis. Some poor prognosis patients accumulated embryos from several cycles and then performed PGS (''embryo banking''). RESULTS: There was no correlation between cohort size of blastocyst analyzed and euploidy rates, but there were significant differences between euploidy rates and maternal age (p< 0.001). Euploidy rates 65%, 56%, 46%, 33%, 19% and 13% for egg donors were observed for ages 42 years old, respectively.The cumulative number of blastocyst needed to produce at least one euploid blastocyst with 95% or higher chance was calculated from single cycles or embryo banking cycles from the same patient and is shown in the below table.

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