Day 5 embryos are given one number and two letters, i.e. 4AA. The first number indicates the stage of development for the embryo: 6=Hatched Blast, 5=Hatching Blast, 4=Fully Expanded Blast, 3=Expanded Blast, 2=Early Blast, 1=Early Blast. The cells making up the blastocyst are represented by the letter: A=Good, B=Fair, C=Poor. The first letter following the number describes the inner cellular mass, the portion of the blast that will develop into the fetus. The second letter following the number represents the quality of the trophectoderm, the portion of the blast that will develop into the placenta. 

We use this system to try to determine which blastocysts will continue development and ultimately lead to a successful pregnancy and healthy child. With that said, just because we grade an embryo as “good” doesn’t mean it will lead to a successful pregnancy, and just because we grade an embryo as “poor” doesn’t mean that it won’t develop into a beautiful baby. The grading is very subjective and we urge clients to not focus all attention on embryo grades.