Grading Scales
Gardner Grading Scale
Blastocysts were given a numerical score from 1 to 6 on the basis of their degree of expansion and hatching status, as follows:
- an early blastocyst with a blastocoel that is less than half of the volume of the embryo;
- a blastocyst with a blastocoel that is half of or greater than half of the volume of the embryo;
- a full blastocyst with a blastocoel completely filling the embryo;
- an expanded blastocyst with a blastocoel volume larger than that of the early embryo, with a thinning zona;
- a hatching blastocyst with the trophectoderm starting to herniate through the zona; and
- a hatched blastocyst, in which the blastocyst has completely escaped from the zona.
For blastocysts graded as 3–6 (i.e., full blastocysts onward), the development of the inner cell mass was assessed as follows:
- tightly packed, many cells;
- loosely grouped, several cells; or
- very few cells.
The trophectoderm was assessed as follows:
- many cells forming a cohesive epithelium;
- few cells forming a loose epithelium; or
- very few large cells
SART Grading Scale
Embryo morphology assessment includes two parts: an Overall Grade and the Stage.
Overall Grade
Overall grade is a subjective assessment of the overall quality of the embryo as good, fair or poor, and is based on assessment of certain characteristics of the embryo such as inner cell mass (ICM) quality or trophectoderm quality.Good: Embryo free of or with only minor imperfection
Fair: Embryo lacking exceptional quality but not excessively imperfect either Poor: Embryo with numerous imperfections
Stage
Stage-dependent grading involves determining the developmental stage of the embryo. Hatching Blastocyst: Embryo, partially or completely free of the zona pellucida, that is composed of trophoblast and inner cell mass (ICM) and a large expanded blastocoel
Expanded Blastocyst: An embryo composed of a number of blastomeres organized around a discernible blastocoel of any size
Early Blastocyst: Presence of a small fluid-filled cavity (blastocoel)
Morula: An embryo in which the blastomeres adhere to each other such that it is not possible to clearly identify individual cells. An embryo undergoing the “compaction” process.
Grade of Inner Cell Mass
Good: An “excellent” to “high quality” ICM with a large number of cells in a single distinct structureFair: An ICM with a moderate number of cells or organization. Lacking exceptional quality but not excessively imperfect either
Poor: An inferior quality ICM. An ICM with few cells or a blastocyst without an identifiable ICM
Grade of Trophoblast
Good: An “excellent” to “high quality” trophoblast with a large continuous and uniform layer of cells in a single distinct structureFair: A moderate number of cells that may have variable size and/or shape
Poor: An inferior quality trophoblast. A trophoblast with few cells or with gaps (non-contiguous layer)