Objective To investigate the influence of inner cell mass and trophectoderm cytoplasmic strings during blastocyst expansion on embryonic development and pregnancy outcome. Methods A retrospective cohort analysis was performed for the clinical data of patients who received pre-implantation genetic testing for aneuploidy （PGT-A） and underwent single blastocyst transplantation in our hospital from June 2019 to December 2021. A total of 530 patients were enrolled，and genetic testing was performed for 2132 blastocysts. According to the presence or absence of cytoplasmic strings during blastocyst expansion，the blastocysts were divided into cytoplasmic strings（+） group with 534 blastocysts and cytoplasmic strings（-） group with 1598 blastocysts，and quality and PGT-A results were compared between the two groups. After the transfer of euploid blastocysts，pregnancy outcome was compared between the 115 blastocysts with cytoplasmic strings and the 415 blastocysts without cytoplasmic strings. Results The rates of cytoplasmic strings（+） in the high-，average-，and low-quality blastocyst groups were 30.19%，24.62%，and 12.63%，respectively. The correlation analysis showed a correlation coefficient of -0.115（P<0.001） between embryo quality and the rate of cytoplasmic strings（+）. There was no significant difference in euploidy rate between the two groups（45.3% vs. 44.6%）. There were no significant differences between the euploid blastocysts with cytoplasmic strings and those without cytoplasmic strings in implantation rate（72.17% vs. 66.02%，P=0.213），miscarriage rate（14.46% vs. 12.77%，P=0.691），and live birth rate（61.74% vs. 57.59%，P=0.424）. Conclusion The presence of cytoplasmic strings is associated with the morphological quality of blastocysts，while it has no impact on embryo ploidy or clinical outcome after euploid embryo transfer. Further research is needed to confirm the impact of cytoplasmic strings on embryonic development.