Objective To investigate the effect of the blastomere number on the 3^rd day of fresh embryo transfer cycles and assisted pregnancy methods on pregnancy outcomes. Methods The data of patients who received embryo transfer for the first time, assisted by conventional in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI), whose embryo quality was gradeⅠor gradeⅡ, and who were admitted to Department of Reproductive Medicine, The First Affiliated Hospital of Naval Medical University (Second Military Medical University) from Jan. 2012 to Aug. 2020 were retrospectively analyzed. A total of 1 788 fresh transfer cycles on the 3^rd day were included and divided into 2 categories:single embryo transfer and double embryo transfer, and each category was further divided into ≤ 6-cell group, 7-cell group, 8-cell group, 9-cell group, and ≥ 10-cell group according to the number of blastomeres. In the fresh single embryo transfer cycles, there were 36 in ≤ 6-cell group (IVF 21, ICSI 15), 53 in 7-cell group (IVF 25, ICSI 28), 204 in 8-cell group (IVF 146, ICSI 58), 36 in 9-cell group (IVF 22, ICSI 14), and 50 in ≥ 10-cell group (IVF 34, ICSI 16). In the fresh double embryo transfer cycles, there were 59 in ≤ 6-cell group (IVF 27, ICSI 32), 72 in 7-cell group (IVF 48, ICSI 24), 1 178 in 8-cell group (IVF 820, ICSI 358), 44 in 9-cell group (IVF 24, ICSI 20), and 56 in ≥ 10-cell group (IVF 24, ICSI 32). The implantation rate, clinical pregnancy rate, live birth rate, and abortion rate were compared. Results In the fresh single embryo transfer cycles, implantation rate and the clinical pregnancy rate in the 8-cell group were significantly higher than those in the ≤ 6-cell, 7-cell, 9-cell, or ≥ 10-cell groups (all P<0.05) and the live birth rate was significantly higher than those in the ≤ 6-cell or 7-cell groups (both P<0.05); there was no significant difference in the abortion rate between 8-cell group and ≤ 6-cell, 7-cell, 9-cell, or ≥ 10-cell groups (all P>0.05); the implantation rate, clinical pregnancy rate, and live birth rate after ICSI embryo transfer in the 8-cell group were significantly higher than those after IVF embryo transfer (all P<0.05), while there were no significant differences in the implantation rate, clinical pregnancy rate, or live birth rate between IVF and ICSI in the ≤ 6-cell, 7-cell, 9-cell, or ≥ 10-cell groups (all P>0.05). In the fresh double embryo transfer cycles, the implantation rate, clinical pregnancy rate, and live birth rate of the 8-cell group were significantly higher than those of the ≤ 6-cell, 7-cell, 9-cell, or ≥ 10-cell groups (all P<0.05), the abortion rate was not significantly different from those of the ≤ 6-cell, 7-cell, or ≥ 10-cell groups (all P>0.05), but was significantly lower than that of the 9-cell group (P<0.05); the implantation rate, clinical pregnancy rate, and the live birth rate after ICSI embryo transfer in the ≤ 6-cell group were significantly higher than those after IVF embryo transfer (all P<0.05), while there were no significant differences in the implantation rate, clinical pregnancy rate, or live birth rate between IVF and ICSI in the 7-cell, 8-cell, 9-cell, or ≥ 10-cell groups (all P>0.05). Conclusion On the 3^rd day of fresh transfer cycles, 8-cell embryos are the first choice, followed by 9-cell, ≥ 10-cell, 7-cell, and ≤ 6-cell embryos. The implantation rate, clinical pregnancy rate, and live birth rate of 8-cell embryos with ICSI are higher than those with IVF, so ICSI can be selected preferentially. For some ICSI assisted pregnancy patients with no other high-quality embryos, transferring ≤ 6-cell embryos can also achieve good pregnancy outcomes.