Evaluation of mouse blastocyst implantation rate by morphology grading

The aim of our study is to observe the relationship between the blastocyst morphology and the implantation rate for mice. Mouse embryos obtained from the superovulated-ICR mice were cultured in vitro from 1-cell zygotes to blastocysts. Mouse blastocysts were then classified into 3 grades: grade I, small blastocysts; grade II, large blastocysts; grade III, hatching blastocysts. They were independently transferred into the uterus of recipient females mated with vasectomized male mice on 96 hours after the zygotes were cultured in vitro. The successful implantation was checked by injection of Chicago Sky Blue 6B on the second day after embryo transfer. Although there was no significant difference in the implantation rates between the grade III and grade II, grade I was significantly decreased, as compared with grade III. Grade I and grade II was also significantly decreased in both the diameter of blastocysts and cell number of inner cell mass (ICM) and trophectoderm (TE), as compared with grade III. These findings indicate that the expanded and hatching blastocyst selections for embryo transfer in in vitro fertilization were evaluated with the high implantation rate.