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Embryo Grading (guest post from Embryoman)

Updated: Aug 6, 2019

Embryo grading! Quite an exciting topic I think!


Everyone (especially embryos) loves to be put in the spotlight and examined under a microscope, right? Especially when it comes to appearances.

And how an embryo looks can tell us quite a bit about how it might perform in making a pregnancy. Better quality embryos have better chances than lower quality embryos.

I’m very excited to be invited by Lucy at Two Lines Fertility to give a guest blog on embryo grading!


So let’s get to it. But first, let’s look at how an embryo typically develops:



On Day 0 (the day of the egg retrieval/insemination), there’s just the one lonely cell. Over the next few days (during the cleavage stage), this cell divides into 2 cells, then 4, then 8, etc. until around Day 4 when the cells start to compact together to form a morula.


Then something interesting happens!

The embryo starts to change and say hello to the blastocyst stage. It’s called a blastocyst because a cavity of water, called a blastocoel, forms within the embryo. At this point the embryo doesn’t look like it did during the cleavage stage. Certain cells become different from one another:



The inner cell mass (ICM) is a wad of cells that goes on to produce the fetus

The trophectoderm is the rest of the cells and these go on to form the placenta

I’ll also take a minute to introduce my stretchy friend the zona pellucida (or zona for short). This is the shell of the embryo, that keeps everything in place and gives protection.

So! That’s how embryos develop. Now let’s talk about how they can be evaluated and graded.

Cleavage stage embryos and blastocyst stage embryos are graded differently.

Cleavage stage embryos are graded on 3 key features:



The number of cells: 4 cells on Day 2 and 8 cells on Day 3, please.

Fragmentation: this is a % of the cells that have broken into tiny pieces

Symmetry: how even the sizes of the cells are


Blastocyst stage embryos are graded on 3 key features and typically reported as an alphanumeric grade (ie. a 4BC)

Expansion (4BC): how big the embryo is (from 1 (small) to 6 (big))

Quality of ICM (4BC): from A (good) to C (poor)

Quality of trophectoderm (4BC): from A (good) to C (poor)


(there was an image here - but I cannot work out how to copy it from Google Docs into this Wix Blog 😥)


So how do these grades relate to success?

Just like in real life, the better looking you are, the more likely you are to succeed. And I guess that’s why I’m here writing guest blogs instead of in the movies.

Just kidding! I am very handsome. But seriously.


A number of studies have been done to show that high quality embryos have a higher chance of making a pregnancy vs poor quality embryos (read more on my blog here).

So does that mean all the unattractive embryos don’t have a shot? NO! They have a chance too, albeit a reduced chance compared to higher quality embryos.


But there’s so much more to success than just embryo grades. The appearance of the embryo is just one part of it.


Implantation, for example, plays a huge role (probably more so than embryo quality). Age also plays a big part: older women can make beautiful embryos - but these will have a lower chance compared to embryos made from younger eggs. These reasons and others are part of why embryo grades don’t matter.


Want to learn more about embryo grading? Check out the Embryo Gallery - a place where people can submit their embryo photos and grades.

Lots of grading statistics and more fun on my blog Remembryo. Follow me on Facebook, Instagram, and Twitter to get your full dose of embryology/IVF information.



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