During IVF it is normal to see a continual drop in numbers in embryo development, which, can lead to the best embryos that will give you your baby.
The appearance or grade of the blastocyst can be used to predict the chance of pregnancy. A blastocyst with a higher grade has a better chance of implanting than one with a lower grade.
When undergoing IVF, a blastocyst is the stage the embryo reaches after 5 days in culture from the egg retrieval. During the three first days of development the embryos start to divide in separate cells, and they are called cleavage embryos. It is only from day 3 to day 5 that the blastocyst is formed.