['To evaluate the relationship between day 3 embryo quality and nucleus spreading rate/signal resolution rate in Fluorescence in situ hybridization (FISH) during the PGD procedure.', "This study was a retrospective data analysis. 367 day-3 embryos were classified based on morphological scoring: grade 1 to grade 4 were defined from worse to better embryo quality. Day 3 embryos were classified as good quality when the number of blastomeres was between 6 and 10 and grade better than 2'. Nucleus spreading rate, signal rate and the full signal rate were compared between embryos with different morphological scoring.", 'Nucleus spreading rate of blastomeres from morphological high-quality embryos was significantly higher (86.25 %) than from poor-quality embryos (76.53 %) (p < 0.05). The rate of blastomeres with full signals was significantly higher (79.32 %) in the morphological high-quality group than in poor-quality group (64.54 %) (p < 0.05). Similar results were found from day 3 embryos with cell number between 6 cells and 10 cells (nucleus spreading rate 86.01 vs. 76.34 %, p < 0.05; full signal rate 78.72 vs. 62.71 %, p < 0.05). Both have no significant difference in the signal rate (82.67 vs. 89.66 %; 83.10 vs. 89.95 %).'] Does morphological good-quality embryo have higher nucleus spreading rate/signal resolution rate in fluorescence in situ hybridization?