To determine the correlation between standard morphology assessment and chromosome constitution in blastocyst analyzed by NGS. Retrospective observational study Data was collected retrospectively from June 2016 to October 2019. In 1221 IVF cycles, 4719 blastocysts were biopsied and analyzed by NGS. DNA from trophectoderm cells were amplified by using Sureplex, hr-NGS was performed with VeriSeq PGS assay, (MiSeq-Ilumina). NGS data was analyzed with Bluefuse sofware (Ilumina). Chromosome constitution was classified according to the genetic results as: euploid, single aneuploid, double aneuploid, complex aneuploidy (>3 chromosomes are aneuploid), (single, double and complex) mosaic, complex mix and mix (aneuploid and mosaic). Embryo morphology was classified as good, fair, or poor based on SART. Descriptive statistics and multilevel model for logistic regression considering a patient as second level and blastocyst as first level were used to evaluate the association between chromosome constitution and embryo morphology which was adjusted by levels of trophectoderm and inner cell mass, maternal age, fertilization technique and day of embryo biopsy. p<0.05 as significant level. All analyses were performed by Stata. For all blastocyst analyzed the frequency was euploid (43.6%), single aneuploid (14.2%), double aneuploid (4.7%), complex aneuploid (2.4%), single mosaic (14%), double mosaic (4.9%), complex mosaic (7.3%), mix (2.9%) and complex mix (5.3%). Most of the embryos biopsied have a good (46.8%) and fair (47.9%) quality and 5.3% were poor quality. Euploidy embryos were associated to have good morphology as is shown in table 1. Interestingly, poor embryo quality have a significantly increased frequency of double aneuploidy (p=0.013). On the contrary, any associations were found for double mosaic, complex aneuploid and mix.Tabled 1Table 1. Association between chromosome constitution and embryo morphologyGoodFairPoorEuploid1092 (53.06%)880 (42.76%)86 (4.18%)OR10.74 (0.65-0.84)**0.70 (0.52-0.94)*Aneuploid301 (44.93%)331 (49.40%)38 (5.67%)OR10.99 (0.82-1.19)0.94 (0.64-1.39)Mosaic290 (43.81%)339 (51.21%)33 (4.98%)OR11.25 (1.03-1.51)*1.25 (0.82-1.89)Double Aneuploid86 (39.09%)109 (49.55%)25 (11.36%)OR11.04 (0.75-1.44)1.94 (1.15-3.26)*Complex Mix79 (31.60%)147 (58.80%)24 (9.60%)OR11.54 (1.13-2.10)**2.03 (1.24-3.33)**OR (IC 95%): Odds Ratio (Confident Interval 95%),* p<0.05, ** p<0.001. Open table in a new tab OR (IC 95%): Odds Ratio (Confident Interval 95%),* p<0.05, ** p<0.001. NGS results confirmed the association between embryonic morphology and euploidy. Mosaicism was reported more frequently in fair embryos, while double aneuploidy and mixed complex are more associated with embryos with low embryo quality.