All you Should Know About Embryo Grading and Success Rates

All you Should Know About Embryo Grading and Success Rates

Infertility is not an end to parenthood. IVF is one of the advanced fertility treatments that can help a couple achieve parenthood. If you are about to take up the IVF process, there are many things that you should know in detail before you proceed. Embryo Grading is one such crucial factor that plays a major part in deciding the success rate of IVF treatment but very few are aware of it.

What is IVF Embryo Transfer?

For this, you should know how an IVF procedure is done. Eggs retrieved from a woman and sperm taken from the male partner are allowed to fertilize in the lab. This results in embryo formation. An embryo is a mass of cells that further grows and divides which when put into a woman’s uterus develops into a baby. This simply emphasizes the importance of selecting the best quality embryo. Only the best embryo can ensure a healthy pregnancy and improve the chance of live birth minimizing the risk of miscarriage.

What is Embryo Grading?

After the fertilization check, embryologists monitor the development of the embryo.   Embryos are evaluated under a microscope based on their appearance, cell shape, number of cells, and several other factors and are graded as good, average, and poor quality. An embryo that has grown up to 3 days is called Day 3 Embryo and one that has grown up to 5 days is called a Blastocyst or Day 5 Embryo.

At 2 stages, embryos are evaluated once at cleavage and another at the blastocyst stage. IVF Embryo transfer is done with a day 3 embryo or a day 5 embryo based on the evaluation.

Grading System: 

The grading system that is followed for Embryo scoring is based on Alpha Consensus, 2011 and David Gardener’s Embryo Assessment criteria.

Cleavage Stage Embryo grading chart (Day 2 and Day 3)

Criteria used:

  1. Number of cells – Embryos that cleave to 4 Cells on Day 2 and 8 Cells on Day 3 are considered the best but not all good embryos follow this pattern. Some embryos may have more or less cell numbers depending on the day but can be selected considering other criteria of Embryo grading. The decision of selecting an embryo rests completely on the wisdom of the embryologist.
  2. Fragmentation – A fragment is defined as an extracellular membrane bound cytoplasmic structure inside an Embryo. The degree of fragmentation is defined as mild (<10%); moderate (10-25%); severe (>25%)
  3. Multinucleation – Multinucleation is defined as the presence of more than 1 nucleus in a cell/blastomere.
  4. Cell Size – All cells / blastomeres in a cleavage stage embryo should be stage specific and evenly sized.

Scoring System of Cleavage Embryo

Grade 1: Good:

  • <10% fragmentation
  • Stage specific cell size
  • No multinucleation

Grade 2: Fair:

  • 10-25% Fragmentation
  • Stage specific cell size for majority of cells
  • No multinucleation

Grade 3: Poor:

  • Severe fragmentation (>25
  • Cell size not specific
  • Evidence of multinucleation

Grade 1 and Grade 2 embryos are considered to be the best and are chosen for embryo transfer. Grade 3 Embryos that have very few cells and heavy fragmentation are considered to be of poor quality.

Blastocyst Stage Embryo (Day 5 or Day 6):

Some of the cells of Day 5 embryos form inner cell mass (ICM) which becomes the fetus and some cells form the trophectoderm epithelium (TE) which becomes the placenta.

On what basis, Day 5 grading is done?

  1. Amount of the blastocyst that has expanded ranging from 1 to 4, 4 is the most developed

1  =  Early – Blastocoel cavity being less than half the volume of the Embryo
2  =  Blastocyst – Blastocoel being greater than half of the volume of Embryo
3  =  Expanded – Blastocoel cavity completely fills Embryo
4  =  Hatched/ Hatching – Fully Expanded blastocyst with embryo partially / fully coming out of zona

  1. Quality of ICM grade ranging from A to C wherein A is considered the best

A – Prominent, easily discernible many cells & tightly packed
B – Easily discernible, many loosely packed cells
C – Difficult to discern with few cells

  1. Quality of TE grade ranging from A to C, wherein A is considered the best

A – Many cells & tightly packed
B – Loosely packed cells
C – Few cells

The first part of the grading is a number followed by 2 letters. Based on this method, in the case of Day 5 grading, for example, if you have a grading like 3AA – this simply means the blastocyst is a good choice for transfer. Embryo transfer is also decided based on the couple’s age, medical history, and some other factors.

To know more about our frozen embryo transfer success rate, check here!

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