Does Embryo Transfer in the Blastocyst Stage Increase the Chance of Implantation and Live Birth? A Study in an Identical Population of Mice

Background: Based on the laboratory assays, there is no definitive decision about embryo selection with the proper embryogenic stage for successful transfer in the in vitro fertilization (IVF) technique leading to live birth. Objectives: This experimental study critically aimed to evaluate the efficacy of embryo transfer in cleavage and blastocyst stages based on the identical population (IP) concept. Methods: The IP concept was explained based on several critical points, including the strain (Balb/c), weight (30 g), age (six and eight weeks for females and males, respectively), number of previous sexual cycles, and the same generation. All embryos in each group were divided into grades A, B, and C. Finally, the produced embryos were transferred by trans-cervical procedure, and the mortality rate was recorded. Results: The number of implantation sites and live births increased in all grades of the blastocyst stage compared to the cleavage stage. The number and percentage of implantation sites in blastocyst and cleavage stages were: [11 (45.83%) vs. 3 (8.57%), P < 0.05] for grade A, [8 (29.62%) vs. 1 (5.26%), P > 0.05] for grade B, [2 (10%) vs. 0 (0%), P > 0.05] for grade C, and number and percentage of live births in blastocyst and cleavage stages were [5 (20.83%) vs. 1 (2.85%), P < 0.05] grade A, [3 (11.11%) vs. 0 (0%), P > 0.05] grade B, and [1 (5%) vs. 0 (0%), P > 0.05] grade C. Conclusions: Based on the results, the frequency of implantation sites and the live birth was higher in blastocyst transfer than in the cleavage stage in IVF.