IVF Babble

Embryo Grading explained

We turned to Embryologist Carolina Andrés at Clinica Tambre and asked her to help us understand what our precious embryos have to do to get good grades!

What is embryo Grading?

Embryo grading is a process performed by the embryologists each day of the embryo’s development since the day of fertilisation. It is used on day 3 and 5 of development to help them establish which embryos they are going to transfer, and on which day. By grading it, it means the embryologist looks at the appearance of the embryo.

It must be said though, that in addition to the grading process, the embryologist also takes into consideration the patient’s age, history and any other relevant information.

Grade A

To get a top-grade A, the embryologist is looking for an embryo, on day 3 that has 6-8 cells which are even in size and without fragmentation if possible. A 10% fragmentation rate still gets you a grade A though.

Grade B

The Grade B embryos have cells that are slightly less even than the grade A. They also have a higher percentage rate of fragmentation. (25-50%)

Grade C

The Grade C embryos show that there is a higher percentage of cellular fragmentation around the cells. (50% or more)

Two days later, on Day 5, the embryologist then moves on to “blastocyst grading”.

What is a blastocyst?

A blastocyst is the term given to an embryo when it reaches a particular developmental form with a fluid filled cavity, a mass of cells (destined to become the foetus) and other surrounding cells (destined to become placenta).

Blastocysts are graded on three factors:

  • The first score is for the expansion of the blastocyst cavity. This is graded on a scale of 1-6. BT5 being the most expanded and BT6 are embryos which have undergone assisted hatched previously.
  • The second score is for the inner cell mass. The embryologist wants to see a tight compaction of cells. This score is actually graded A, B, C or D with A being the best.
  • The third score is for the appearance of the trophectoderm (the part that makes the placenta). Again, this score is marked with an A, B, C or D; with A being the best.

Understanding the grade

When you see your embryo grade, you will see a number followed by a letter.

The blastocyst grading evaluates the physical appearance of the blastocyst in the moment of the evaluation. However, the quality in day +3 would be taken into consideration when choosing which embryo is going to be transferred first.

Low grade embryos are discarded since their chances of implantation are lower, as well as their survival rate after vitrification.

Thank you so much Clinica Tambre. If you have any questions for Embryologist Carolina Andrés or the rest of the team, click here

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