This study aimed to explore the effects of low-concentration (0.6 ng/mL) granulocyte-macrophage colony-stimulating factor (GM-CSF) supplementation on human embryo quality and pregnancy outcomes in patients with fresh transfer cycles. The data were retrospectively collected from 719 hyperstimulation cycles of 631 patients divided into two groups: GM-CSF supplementation (0.6 ng/mL,  = 399) and control ( = 320). The embryo quality and pregnancy outcomes were compared. GM-CSF addition significantly increased the available embryo rate (52.0 vs. 48.1%,  < .05). In patients >38 years, it significantly enhanced cleavage (99.4 vs. 97.8%,  < .05) and blastocyst formation (45.7 vs. 34.9%,  < .05) rates but not pregnancy outcomes, including clinical pregnancy (power = 0.160) and implantation (power = 0.204) rates. The lack of a statistically significant difference could be related to low study power. These results suggest that low-concentration GM-CSF addition contributes to embryo quality improvement, especially in patients >38 years. IMPACT STATEMENT Granulocyte-macrophage colony-stimulating factor (GM-CSF) has a beneficial effect on the development of human embryos in assisted reproductive technology. Adding 0.6 ng/mL GM-CSF significantly increased the available embryo rate. In patients over 38 years of age, it statistically significantly enhanced the cleavage rate (99.4 97.8%,  < .05) and blastocyst formation rate (45.7 vs. 34.9%,  < .05). GM-CSF benefits embryos with poorer development potential and a randomised clinical trial with a larger sample size should be performed.