How Embryo Grading is done

HOW EMBRYO GRADING IS DONE?

In IVF treatments, embryologists make classifications according to certain criteria every day from the collection of the oocyte to the development of the embryo from day 0 to day 6. The main objective here is to reach the embryo with the highest growth potential, which is thought to be the highest chance of pregnancy.

HOW 0th DAY GRADING IS DONE?

The day of oocyte (ovo) collection is considered to be day 0. Procedures on that day can be listed as follows: The oocytes are collected and rested in the laboratory for 3 hours on special devices. The denudation is purified from the surrounding cells and classified according to their maturity, with the placement of a sperm cell in each mature oocyte, ie microinjection.

WHIC OOCYTES CAN BE MICROINJECTED?  

For fertilization, the ovo cells must be mature MII (metaphase II oocyte), that is to say that the meiotic division has reached the 2nd phase.

HOW TO DETERMINE THE MATURITY OF OOCYTES?

GV (GERMINAL VESICULAR) OOCYTES: These oocytes are immature ovo cells that have not yet begun meiosis. These cells cannot be fertilized.

MI (METAPHASE I ) OOCYTES:These are immature oocytes that have paused in the Ist phase of meiosis. If they are not mature enough, they can be matured and fertilized by waiting for 4 hours under appropriate conditions.

MII (METAPHASE II ) OOCYTES:These are mature oocytes ready to fertilize in the IInd phase of meiosis.

GV OOCYTE                                                           MI OOCYTE

MII OOCYTE

HOW TO DETERMINE WHETHER OOCYTES ARE OF GOOD, MEDIUM OR POOR QUALITY?

GOOD QUALITY OOCYTES:

• Transparent cytoplasm and normal shape
• Single and smooth polar body
• Outer layer of transparent and normal thickness (zona pellucida)

MEDIUM QUALITY OOCYTES:

• Slight granulated cytoplasm and/or deformed shape
• Polar body in fragmented and abnormal morphology
• Mild pigmented deformed outer layer
• Cytoplasmic bodys
• Debris in the perivitellien area (between the oocyte membrane and the outer layer)

POOR QUALITY OOCYTES:

• Dark/granular/deformed cytoplasm
• Polar body in fragmented and abnormal morphology
• Pigmented/thick zone
• Vacuoles
• Perivitelline debris

HOW THE 1st DAY FERTILIZATION CONTROL  IS PERFORMED?

Impregnation may bee seen 16-22 after insemination. Fertilization is basically the combination of the nucleus from a sperm and the nucleus from the oocyte. For a normal fertilization, it is necessary to see the presence of two pronuclei and two pole bodies from both male and female. The presence of one pronucleus or more than two pronucleus is called abnormal fertilization.

Evaluation criteria at this stage of development:

• Number, size and position of pronuclei
• Number, distribution and size of nucleolus precursor bodies (NPB)
• Number and location of polar bodies

Normally fertilized oocytes (2PN and 2 polar bodies)

HOW II-III.rd DAY EMBRYO GRADING IS DONE?

On the second day of development, on approximately 22-25th hour, single-cell zygote is divided into two stages. They turn into a four-cell embryo at 42-44 hours. On day 3, the embryo continues to divide. They reach the 6 to 8 cell stage in 66-68 hours. We classify embryos according to some criteria in this period, which we call early division stage.

• Good quality embryo: cells of equal size with transparent cytoplasm
• Medium quality embryo: with cytoplasmic irregularities and/or slightly different cell sizes
• Poor quality embryo: cell sizes are significantly different from each other and/or have granular or dark cytoplasm

As the cells divide, some cytoplasm residue may accumulate in the cell. The rate and position of these structures, which we call fragmentation, in the embryo are important for the evaluation of embryo quality.

• 1st quality embryo: no fragmentation
• 2nd quality embryo: % <10><!--10--><!--10--><!--10--><!--10--><!--10--><!--10-->
• 3rd quality embryo: -35 fragmentation
• 4th quality embryo: >35% fragmentation

The decrease in embryo quality in the early stage in terms of the specified parameters causes the development of the advanced stage to halt or poor development.

2nd day 1st quality embryo (with 4 cells)     3rd day 1st quality embryo (with 8 cells)

2nd day 3rd quality embryo              3rd day 2nd and 3rd quality embryos

IV. II-III.rd DAY EMBRYO GRADING IS DONE?

 At 96 hours following fertilization, the embryo becomes a multicellular cell with 16-20 cells, the cell borders of which are now becoming extinct.

4th day 2nd quality embryo (Morula)                          4th day 1st quality embryo slitting

HOW 5th/6th  DAY EMBRYO GRADING IS DONE?

The embryo, which reached the level of 5 and 6 days, is at the stage we call the blastocyst with two differentiated cell layers containing an average of 100 cells. The internal cell mass (ICM) in these two different cell layers is the part that makes up the baby. The external cell mass (trophectoderm) forms the placenta. The quality of the embryo at this stage is determined by the characteristics of the internal and external cell masses and the expansion of the embryo. Accordingly, blastocysts are classified as follows:

ACCORDING TO THE EXPANSION OF INNER CAVITY OF THE EMBRYO (BLASTOCOELE)

SCORE 1:   Beginning of cleavage in the embryo. Blastocoele (inner cavity) is less than half of cell volume

SCORE 2:Blastocoele is more than half of cell volume

SCORE 3:Blastocoele volume covered the volume of the embryo

SCORE 4:Blastocoele volume is larger than the volume of the embryo and the outer membrane is thinner

SCORE 5:The outer membrane breaks and the embryo starts to burst

SCORE 6: The embryo is completely separated from the outer membrane.

CLASSIFICATION ACCORDING TO INNER CELL MASS (ICM):

A:Contains a large number of tightly packed cells

B:Contains loose packaged but many cells

C:Contains loose and very few cells

CLASSIFICATION ACCORDING TO OUTER CELL MASS (TROPHECTODERM):

A:Contains tightly connected, a large number of properly sorted cells

B:Containing a small number of loosely bound cells

C:Contains irregularly sorted loosely bound large cells

5th day 5AA embryo                                                 6th day 6AA embryo