Embryo Grading

Embryo Grading Process

During the process of Embryo Implantation in IVF, the embryos are cultured for around six days and during that period they receive quality grades every day.

Embryo-Grading

Egg Retrieval and Insemination Day 0

The maturity of the egg is important as a mature egg has the best chance of getting fertilized. The three different stages of egg maturation are:

  • Germinal vesicle (GV): It is the stage where the egg has not begun meiosis till now and is thus considered immature.
  • Metaphase I (MI): This is the first phase of the egg is meiosis, but is not completely mature yet as it has not entered the second phase of meiosis. This type of immature egg matures after being in temperature-controlled incubation for a couple of hours.
  • Metaphase II (MII): This is the second phase of meiosis of the egg, which is mature by now. Eggs at this stage are ready for fertilization and have the following characteristics.

Good

  • Clear cytoplasm/normal shape
  • Single differentiated polar body
  • Thin/clear zona pellucid

Fragmented/abnormal polar body

  • Slightly pigmented/amorphous zona
  • Fragmented/abnormal polar body
  • Slightly pigmented/amorphous zona
  • Cytoplasmic bodies
  • PV debris

Poor

  • Dark/grainy cytoplasm/misshapen
  • >1 polar body structure
  • Pigmented/thickened zona
  • Vacuoles
  • PV debris

Fertilization Check Day One

Fertilization can be seen clearly after 16 to 22 hours after the process of insemination. Normal fertilization can be seen by exactly two pronuclei in the center of a one-celled zygote. Fertilization is not abnormal when there is a single pronucleus and when there are more than two pronuclei present.

Multicell Grading Day Two/Three

On day two the single-cell zygote should divide into an embryo (approx. two to four cells). On day three the embryo should continue to divide (four to eight cells).

Embryo Quality:

Good: have a clear cytoplasm with symmetrical cells
Fair: these cells are slightly asymmetrical having slight cytoplasmic irregularities
Poor: these cells are quite asymmetrical and might have grainy and dark cytoplasm
A = No fragmentation
B = <10% fragmentation
C = 10-35% fragmentation
D = >35% fragmentation

Day Four

On the 4th day, the transition of embryos begins from a multi-cell embryo to a highly advanced developmental stage. Embryos then start compacting and forming morulae. Cells of a morula-stage embryo are not quite distinct like the previous days, and hence these embryos fail to receive quality grades.

Day Five/Six Blastocyst Stage

A blastocyst is a developed embryo that comprises two different cell types: one group of cells is referred to as the inner cell mass, which forms the fetal tissue, and another group of cells, known as the trophectoderm, helps in the formation of the placenta. Blastocysts are graded on the basis of their expansion (early, expanding, expanded, and hatching) as well as on the basis of the quality of these two different cell types (graded on a good-fair-poor scale). Blastocysts that are good or even fair in quality can be frozen.

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