OBJECTIVE: PGS for aneuploidy in women with recurrent pregnancy loss is controversial. One limitation of PGS using FISH is the limited number of chromosomes tested. SNP microarrays simultaneously test all 23 chromosomes from any embryonic cell. However, little data exists on the diagnostic improvement using SNP microarrays compared to FISH. The aim of this study was to test the hypothesis that using SNP microarrays increases diagnostic accuracy over 10-probe FISH.DESIGN: Retrospective study.MATERIALS AND METHODS: All patients referred for PGS from January 1 to April 15, 2010 with a history of ≥2 pregnancy losses were included. Four patients were tested by trophectoderm biopsy and all other patients had day-3 blastomere biopsy. 23-chromosome SNP microarray testing was used for each embryo. Prior to the availability of SNP microarray technology, we used 10-probe FISH for aneuploidy screening, testing chromosomes 13, 14, 15, 16, 17, 18, 21, 22, X, and Y. In order to measure the diagnostic improvement using SNP microarrays, we calculated the percentage of aneuploid embryos that would have been missed by 10-probe FISH.RESULTS: A total of 34 patients and 372 embryos were tested. Mean maternal age was 37 ± 4.7 years and the average number of embryos tested was 10.9 ± 6.1. Using SNP microarrays, 56% (210/372) of the embryos were diagnosed as abnormal and 3.4 ± 2 euploid embryos were identified per patient. 13.3% of aneuploid embryos diagnosed by SNP microarrays would have been missed by 10-probe FISH. If 10-probe FISH had been used, 19.4% of FISH-diagnosed normal embryos would have been recommended for transfer when, in fact, they were aneuploid for untested chromosomes. In 23.5% of patients, FISH would have wrongly diagnosed 25% or more of the embryos as normal, with the highest error rate at 100%.CONCLUSION: PGS with SNP microarrays is diagnostically superior to 10-probe FISH. This improved accuracy of SNP microarrays may improve pregnancy outcomes. OBJECTIVE: PGS for aneuploidy in women with recurrent pregnancy loss is controversial. One limitation of PGS using FISH is the limited number of chromosomes tested. SNP microarrays simultaneously test all 23 chromosomes from any embryonic cell. However, little data exists on the diagnostic improvement using SNP microarrays compared to FISH. The aim of this study was to test the hypothesis that using SNP microarrays increases diagnostic accuracy over 10-probe FISH. DESIGN: Retrospective study. MATERIALS AND METHODS: All patients referred for PGS from January 1 to April 15, 2010 with a history of ≥2 pregnancy losses were included. Four patients were tested by trophectoderm biopsy and all other patients had day-3 blastomere biopsy. 23-chromosome SNP microarray testing was used for each embryo. Prior to the availability of SNP microarray technology, we used 10-probe FISH for aneuploidy screening, testing chromosomes 13, 14, 15, 16, 17, 18, 21, 22, X, and Y. In order to measure the diagnostic improvement using SNP microarrays, we calculated the percentage of aneuploid embryos that would have been missed by 10-probe FISH. RESULTS: A total of 34 patients and 372 embryos were tested. Mean maternal age was 37 ± 4.7 years and the average number of embryos tested was 10.9 ± 6.1. Using SNP microarrays, 56% (210/372) of the embryos were diagnosed as abnormal and 3.4 ± 2 euploid embryos were identified per patient. 13.3% of aneuploid embryos diagnosed by SNP microarrays would have been missed by 10-probe FISH. If 10-probe FISH had been used, 19.4% of FISH-diagnosed normal embryos would have been recommended for transfer when, in fact, they were aneuploid for untested chromosomes. In 23.5% of patients, FISH would have wrongly diagnosed 25% or more of the embryos as normal, with the highest error rate at 100%. CONCLUSION: PGS with SNP microarrays is diagnostically superior to 10-probe FISH. This improved accuracy of SNP microarrays may improve pregnancy outcomes.