What’s My Grade Again?
At IVF clinics, transfer day is the long awaited day that those who have made it to, may see as the penultimate step to achieving their goal. And in the world of fertility, live birth of a healthy child is the goal. Different clinics have different ways of conducting transfers. Some may do this in the OR, some have dedicated rooms for transfers, some have the embryologist in the room, some don’t. In my experience as an embryologist, I prefer to be in the room during transfers because this is often the only time we embryologists get a glimpse into the lives of our patients. While it can be nerve wracking with everyone watching you while you quite literally work under a microscope, the payoff is feeling the spark of hope and excitement as this may be the moment when a family begins or completes their journey.
So when a patient asks “what’s the grade of my embryo?” or “what does this grade mean?”, and “how likely is it that an embryo of this grade will implant”, typically the doctor will have an answer that is intended to assuage any fear, hesitation, or disappointment. This is a delicate dance because many of our patients have experienced a myriad of letdowns, disappointments, and heartbreak up to this point. But I’m one of those people that believes more information is always better, and I’m guessing there are patients out there who think the same way. And I also believe that the more you can get the technical and anxiety driving thoughts out of the way prior to transfer day, the better the transfer will go since you can then focus on the good parts, like where you’ll be getting fries after.
So what do grades really mean?
Most embryology labs will have their own interpretation of the Gardner grading system. This is a method of embryo grading developed by David Gardner, to describe blastocyst expansion, the ICM, and the trophectoderm. This system doesn’t fully hold up to today’s protocols because some of what we do in the lab with embryos wasn’t done when this system gained popularity, but most labs have some iteration of this. Another significant thing to consider is that currently, almost all labs are grading embryos manually. Meaning individual embryologists are using their eyes and experience to grade, so naturally there’s a large range in how people grade. There is technology in development to allow artificial intelligence to create a more standardized method for grading, but this simply isn’t something that is readily or commercially available as of 2024.
Expansion: typically graded from 4-6. This can refer to how cellular the blastocyst is. During development, the cells of the embryo are continuously dividing and growing. Imagine a beachball - there are a few different segments you can see, differentiated by different colors. Imagine each of these segments is a cell. Now imagine a soccer ball. A soccer ball has many more smaller segments. So a beach ball may be something we’d call grade 4 expansion, while a soccer ball may be a grade 6 expansion. What embryologists look for is cellularity, symmetry, overall size, and whether the embryo has hatched out of the zona.
ICM: the ICM grade is the first letter in an embryo grade. The ICM is the “inner cell mass” of the embryo, what will eventually become the fetus. This ranges from A, B, C, and D. You will not see a grade D on an embryo being transferred, as this indicates either the absence of this component of the embryo, or that it is degenerated or atretic, aka, dead. The grading of an ICM can refer to size, compaction or how dense the cells appear, and how defined the borders of the ICM are.
Trophectoderm: the trophectoderm comprises the bulk of what you generally see when looking at an embryo. This portion can look almost like tiles. The trophectoderm cells are what will eventually become the placenta. These cells are responsible for attaching to the wall of the uterus. Sometimes you’ll hear a doctor or embryologist say they like “sticky” embryos, meaning we want the troph cells to be healthy and ready to attach. The grading of the troph refers to just how many there are (cellularity), and how symmetrical and healthy they appear.
Day: the day of development of your embryo is not generally included when disclosing embryo grades, however to an embryologist, this can be a significant metric in assessing the potential for success of an embryo.
So is a 4CC worse than a 5AA?
Hrmmmm, this is an interesting question. Recently I heard this question asked during a transfer, and the doctor’s response was really great food for thought. He said “well, there’s about a 60% chance of implantation, but in reality it’s either 0% or 100%.” I keep thinking back on that. Many embryologists track their own rates, for the sake of curiosity and also for the sake of quality control. We’re heavily invested in the follow through, and actuating success for our patients. My implantation rate sits pretty steadily around 82%. But the concept of, you either are or you aren’t, hit different. All this to say that yes, technically speaking, we do like to see AA grades of course, this usually draws up images in our minds of beautiful expanded blastocysts with nice compacted ICMs and symmetrical small troph cells. And we shudder a little at the idea of thawing a day 7 grade 4CC embryo. However, and this is a BIG however, we’ve seen every exception to the rules. There are plenty of patients who for whatever reason, don’t get pregnant from their textbook gorgeous 5AA embryos, and there are patients who have beautiful healthy babies from the day 7 4CCs.