AbstractBackgroundAdvances in cell culture media have led to a trend of embryo transfer from the early cleavage stages to blastocyst stage.ObjectiveThe study aims to compare the effects of fresh embryo transfer in cleavage and blastocyst stage on pregnancy outcomes.Materials and MethodsThis cross-sectional study was conducted on 1422 cases referred to the Umm-al-Banin Infertility Clinic Center, Dezful, Iran, between July 2013 and December 2020 who were candidates for in vitro fertilization/intracytoplasmic sperm injection for fresh embryo transfer. A total of 1246 cases were divided into 4 categories on days 2-5 or 6. Chemical and clinical pregnancy, abortion, multifetal pregnancy, ongoing pregnancy, and live birth rates were analyzed.ResultsFresh embryo transfer was performed in 28.5% of the cases on the 2ndday, 45.8% on the 3rd, 15.3% on the 4thday, and 10.4% on days 5 or 6. The overall clinical pregnancy and live birth rates were estimated at 20.6% and 17.6% in the cleavage, and 17% and 14% in the blastocyst stages, respectively. However, no significant difference was observed in either group. In addition, there was no significant difference between groups in terms of the abortion, multifetal pregnancy, and ongoing pregnancy rate (p>0.05).ConclusionAccording to the results, the consequences of pregnancy in fresh embryo transfer at the blastocyst stage were not superior to embryo transfer at different stages of the cleavage process.