What Is A Blastocyst?
During conception inside a woman's body, the egg is fertilized by sperm in the fallopian tube and an embryo is formed. Eggs are retrieved from a woman's ovaries, fertilized with sperm, and an embryo is created. The embryo divides and multiplies its cells over 5 to 6 days to become a blastocyst. Embryos that survive to this stage of development have a high implantation potential once transferred into the uterine cavity.
The embryo has the appropriate cell number for stage of development (eg., on day three, embryos should have 8 cells, also known as blastomeres) and the cells are even in their size and shape. The embryos should have little or no fragmentation (small amounts of extracellular debris) between cells.
The embryo has the correct development of cell numbers (6-8 cells on day three), with a small amount of fragmentation (20% fragmentation), or slight uneveness of blastomere sizes. grade 3 the embryo contains blastomeres that are uneven in size and has more than 30% fragmentation. embryos developing slowly will also receive a grade of 2 or 3 even if they are normal otherwise. grade 4 the embryo contains very few, if any, viable appearing cells and has a high percent fragmentation (over 50%).