Blastocyst grading is not an exact science, but it is a tool that providers use in addition to other factors to determine which embryos may be fit for transferring. Despite forty years of research and clinical application, the average success rate of IVF today has been reported to be as low as 20-40%. Selection of the best embryo is key to the success of IVF cycles.
Blastocysts possess an inner cell mass which will become the baby. The outer layer of cells of the blastocyst are called the trophoblast. The trophoblast will become the placenta.This layer surrounds the inner cell mass and a fluid-filled cavity known as the blastocoel. Blastocysts are qualified by their inner cell mass and trophoblast.
Rating blastocysts follows a three-part system of grading, however there are many systems of grading.
The three parts are always:
-The degree of the expansion of the embryo’s cavity.
-The inner cell mass (the baby-making part) quality.
-The trophectoderm quality (the cell layer that makes the placenta and the membranes surrounding the baby).
The number and quality of blastocysts available is a key determinant for a patient’s chance of success with ART, thus blastocyst development rate is an important measure of an IVF clinic’s performance. While morphological evaluation is widely accepted and implemented in most IVF clinics worldwide, the exact morphologic parameters used to score embryos are highly variable between clinics, and the assessment process is strikingly subjective even between embryologists at the same clinic. Embryo grading is not the end all and be all though- every embryologist has stories of remarkable transfer outcomes with poor quality embryos!
However, most human embryos do not have the genetic potential to develop normally to the blastocyst stage, hatch from their shells, implant, and continue normal embryonic development in order to result in a live birth.