Purpose <p>To evaluate the euploidy rate and obtain the biochemical pregnancy, implantation, clinical pregnancy, miscarriage and live birth rates for embryos biopsied on days 5, 6, 7 and 8 of development.</p> Methods <p>Observational, retrospective and multicenter study. In total, 1845 IVF‒ICSI cycles with preimplantation genetic testing for aneuploidy (PGT-A) were included. The euploidy rate was determined according to the biopsy day (5, 6, 7 or 8), as were the reproductive outcomes of 710 single embryo transfers (SETs).</p> Results <p>Seven thousand three hundred thirty-eight biopsied embryos were analyzed by means of PGT-A. Of these, 414 procedures resulted in amplification failure (5.6%), leaving 6924 embryos. In total, 5042 (72.8%) were biopsied on day 5, 1779 (25.7%) on day 6, 101 (1.5%) on day 7, and 2 (0.03%) on day 8. The euploidy rates on days 5, 6, 7 and 8 were 41.6%, 32.7%, 27.7%, and 50%, respectively. The euploid embryo biopsied on day 8 was not transferred. For blastocysts biopsied on days 5, 6 or 7, the biochemical pregnancy rates were 62.3%, 53.2% and 33.3%; the implantation rates were 59.8%, 50.3% and 22.2%; the clinical pregnancy rates were 59.7%, 42.2% and 22.2%; the live birth rates were 52.5%, 43.2% and 22.2%; and the miscarriage rates were 12.2%, 14.0% and 0%, respectively.</p> Conclusions <p>The euploidy rate decreased with increasing time required to reach the blastocyst stage. Compared with day 6 and day 7 euploid embryos, day 5 euploid embryos had better clinical outcomes. However, the findings in this study demonstrate that embryos with slow development can result in live births.</p> Clinical trial registration <p>Due to being a retrospective study, the clinical trial was not registered.</p>