Embryo Grading in IVF Made Simple: What You Need to Know


There is still a lot of confusion in patients' minds about embryo quality and embryo grades. Part of the problem is that IVF doctors are not very transparent and will not share photographs of your embryos with you or explain to you what the grade means. In fact, many IVF clinicians are quite clueless about how to grade embryos, because they don’t spend any time in the IVF lab, and leave the grading up to their embryologist.

Most doctors will usually just airily say – You have top-quality embryos and a good chance of getting pregnant! When the patient asks for a treatment summary, they will claim that the embryo they transferred was a 2AA blastocyst, but without a photo, it’s hard to trust this statement.

Unfortunately, most patients aren't sophisticated enough to ask intelligent questions or demand documentation, which is why IVF clinics get away with this.

Let’s start from the basics.

It’s important for us to grade embryos because it allows us to be able to estimate what the chances of that embryo becoming a baby are. But you need to remember that not every good quality embryo becomes a baby, because implantation is still a black box area. And even if an embryo is of top quality, it may not necessarily be genetically normal. Even doing a PGD doesn't help because even though the embryo may be chromosomally normal, this doesn't mean that it does not have a lethal genetic defect and will not implant. This means that no matter what grade we assign to the embryo in the lab by eye-balling it, in real life, the only good quality embryo is the one that becomes a baby – and we're still not very good at predicting this!

We can provide statistics and estimate probabilities, and we know that the chance of a 3AA embryo implanting is better than the chance of a 1BB becoming a baby. But the reality is that statistics don't apply to individuals - they only apply to groups of patients. And we've seen that even poor quality low-grade embryos do become babies.

The good news is that these are completely normal babies, so please stop worrying that a “poor quality embryo” will become an abnormal baby. The outcome is binary, and if it implants, it's a perfectly healthy baby. But the chances are higher that it will not implant, as compared to a good-quality embryo. The trouble is that when we transfer a poor-quality embryo and the patient has a miscarriage, she always blames the embryo, but that is not true. Please understand that embryo grades are just medical shorthand which embryologists use in order to communicate to each other what the embryo looks like. But it doesn't really mean anything more as far as the clinical outcome is.

One of the other major reasons for confusion is that patients don't understand how embryos are graded – and this is especially true for blastocysts, where the grading is fairly complex. Let’s compare a 1AA blastocyst with a 3AA blastocyst for example. Typically, we believe that a Number 1 embryo is better than a Number 3 embryo – after all, we all prefer toppers. But, for blastocyst grading, it's exactly the opposite! A 5AA embryo is much better than a 1AA embryo! To understand this, let’s review how a blastocyst develops. A morula on Day 4 is a ball of cells, and when it starts absorbing fluid from the surrounding environment, it transforms itself into a blastocyst. This absorbed fluid collects to form a cavity called a blastocele, and when this happens, the embryo is now called a blastocyst ( which is just a synonym for an embryo on Day 5).


When the cavity is small, it's called a 1AA embryo, where number 1 describes the size of the cavity. What about the letters? What do they mean? The first A denotes the quality of the cells in the inner cell mass (ICM) – that part of the embryo that becomes a baby. The second A represents the quality of the trophectoderm (TE) – the part of the embryo that is destined to become the placenta. I understand these are technically complicated words, but it's easy to do a Google search and learn more about this. As the blastocyst keeps on developing, its cells absorb more fluid, as a result of which the size of the cavity will keep on increasing. When the cavity is more than half the size of the blastocyst, it's called a 2AA blastocyst. And when it grows even more, which means that it's mostly just a cavity and the cells just form a thin rim around this, it is called a 3AA blastocyst. As it grows, it keeps on absorbing more fluid and starts expanding, when it’s called a 4AA blast.


Blastocyst Grade 1AA


Blastocyst Grade 2AA


Blastocyst Grade 3AA


Blastocyst Grade 4AA

So why is the blastocyst doing this? Remember that it’s covered by a shell called a zona, and for the embryo to implant, it needs to crack this zona so that it can make contact with the endometrium. This is nature's ingenious mechanism which allows for the embryo to hatch from its shell.

By absorbing the fluid, the size of the cavity keeps on increasing, and this hydraulic force allows it to burst the zona, which allows the blast to hatch without causing any damage to the embryonic cells themselves.

Hatching Blastocyst


Blastocyst Grade 5AA

Completely Hatched Blastocyst


Blastocyst Grade 6AA

This really is a little bit of a miracle, and I still marvel at the magic of how babies are made!

Authored by : Dr Aniruddha Malpani, MD and reviewed by Dr Anjali Malpani.