Blastocysts are Day 5 Embryos, wherein they have more than 100 Cells in them.
A blastocyst is the final stage of the embryo's development before it hatches out of its shell (zona pellucida) and implants in the uterine wall.
BLASTOCYST GRADING
This blastocyst grading system assigns 3 separate quality scores to each blastocyst embryo:
- Blastocyst development stage - expansion and hatching status
- Inner cell mass (ICM) score, or quality
- Trophectoderm (TE) score, or quality
- Blastocysts are given a quality grade for each of the 3 components and the score is expressed with the expansion grade listed first, the inner cell mass grade listed second and the trophectoderm grade third. For example, a blastocyst quality grade of 4AB means that the blastocyst is expanded (grade 4), has many tightly packed cells in the inner cell mass (grade A), and has a trophectoderm with few cells forming a loose epithelium (grade B). See the examples of blastocyst grading pictures below.
Expansion
grade
Blastocyst development and stage status
1
Blastocoel cavity less than half the volume of the embryo
2
stocoel cavity more than half the volume of the embryo
3
Full blastocyst, cavity completely filling the embryo
4
Expanded blastocyst, cavity larger than the embryo, with thinning of the shell
5
Hatching out of the shell (Zona)
6
Hatched out of the shell (Zona)
ICM
grade
Inner cell mass quality
A
Many cells, tightly packed
B
Several cells, loosely grouped
TE
grade
Trophectoderm quality
A
Many cells, forming a cohesive layer
B
Few cells, forming a loose epithelium
EARLY BLASTOCYSTS
Early Blastocysts with Very little Cavity (Blastocele) (Cant Grade them)
(C) Cavity is Very Small
(I) Inner Cell mass : Can’t Grade
(T) Trophectoderm : Can’t Grade
EARLY BLASTOCYSTS
Blastocysts with Cavity (Blastocele) less than ½ Volume of Embryo (Grade1)
(C) Cavity < ½ Embryo’s Volume Volume = Grade 1
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)
(C) Cavity < ½ Embryo’s Volume = Grade 1
(I) Inner Cell mass = Grade A (very Good)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity < ½ Embryo’s Volume = Grade 1
(I) Inner Cell mass = Grade B (Poor)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity < ½ Embryo’s Volume = Grade 1
(I) Inner Cell mass = Grade C (Very Poor)
(T) Trophectoderm = Grade C (Very Poor)
INTERMEDIATE STAGE BLASTOCYST
Cavity (Blastocele) will be More than ½ the Volume of Embryo (Grade 2)
(C) Cavity > ½ Embryo’s Volume = Grade 2
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)
(C) Cavity > ½ Embryo’s Volume = Grade 2
(I) Inner Cell mass = Grade A (very Good)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity > ½ Embryo’s Volume = Grade 2
(I) Inner Cell mass = Grade B (Poor)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity > ½ Embryo’s Volume = Grade 2
(I) Inner Cell mass = Grade C (Very Poor)
(T) Trophectoderm = Grade C (Very Poor)
INTERMEDIATE STAGE BLASTOCYST
Cavity (Blastocele) will completely fill the Volume of Embryo (Grade 3)
(C) Cavity Completely Fills Embryo = Grade 3
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)
(C) Cavity Completely Fills Embryo = Grade 3
(I) Inner Cell mass = Grade A (very Good)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity Completely Fills Embryo = Grade 3
(I) Inner Cell mass = Grade B (Poor)
(T) Trophectoderm = Grade B (Poor)
(C) Cavity Completely Fills Embryo = Grade 3
(I) Inner Cell mass = Grade C (Very Poor)
(T) Trophectoderm = Grade C (Very Poor)
Fully Expanded Blastocyst (Grade 4)
Large, well expanded
(C) Completely Expanded = Grade 4
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)
(C) Completely Expanded = Grade 4
(I) Inner Cell mass = Grade A (very Good)
(T) Trophectoderm = Grade B (Poor)
(C) Completely Expanded = Grade 4
(I) Inner Cell mass = Grade B (Poor)
(T) Trophectoderm = Grade B (Poor)
(C) Completely Expanded = Grade 4
(I) Inner Cell mass = Grade C (Very Poor)
(T) Trophectoderm = Grade C (Very Poor)
HATCHING BLASTOCYST (GRADE 5)
BLASTOCYST HATCHING OUT OF ZONA
Blastocyst Hatching out of Zona (shell) = Grade 5
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)
COMPLETELY HATCHED BLASTOCYST (GRADE 6)
Blastocyst completely hatched = Grade 6
(I) Inner Cell mass = Grade A (Very Good)
(T) Trophectoderm = Grade A (Very Good)