If you’re going through IVF, you’ve probably heard your medical team mention “embryo grading.” But what does this grading really mean, and how does it impact your success in IVF? Today, embryologist Alease Barnes takes us behind the scenes to understand how embryos are graded in the lab and why these details matter for your journey.
What Is Embryo Grading?
During an IVF cycle, the lab team will combine eggs and sperm and let them grow in culture for about five to seven days. By days five, six, or seven, these fertilized eggs reach what’s called the “blastocyst stage.” This is when Alease and her team grade the embryos, identifying the best-quality ones for transfer.
The Three Key Parts of Embryo Grading
When grading embryos, embryologists look at three main features:
- Expansion: This refers to the size of the embryo. Larger embryos are closer to hatching, which is an important step for implantation.
- Inner Cell Mass (ICM): The ICM is the clump of cells that will eventually form the baby. If you’ve ever seen an embryo under a microscope, it’s the tight bundle of cells on one side of the embryo. ICM is graded on a scale of A to D, similar to school grades—A is ideal, and D is the lowest grade. For high-quality ICM, embryologists look for compact cells with minimal cell death.
- Trophectoderm: Surrounding the ICM is the trophectoderm, the layer of cells that will develop into the placenta. A healthy trophectoderm should have a “cobblestone” appearance—lots of plump cells with no gaps. Like the ICM, the trophectoderm is graded from A (best) to D (least ideal).
Understanding Embryo Grades: What Do “4AB” and “3BC” Mean?
Embryos are assigned a grade combining numbers and letters, such as “4AB” or “3BC.”
The number reflects the embryo’s stage of expansion, while the first letter is the grade for the Inner Cell Mass (ICM), and the second letter is the grade for the trophectoderm.
Here’s a general breakdown of how the letters translate to embryo quality:
- Good quality: AA or AB
- Fair quality: BA or BB
- Poor quality: BC, CB, CC, or anything lower
A good-quality embryo with an “AA” or “AB” grade has the best chance of success, but even fair or poor-quality embryos can still lead to healthy pregnancies.
What is The Best Embryo Grade?
The ideal embryo grade is AA, indicating that both the ICM and the trophectoderm are high-quality. This doesn’t guarantee a successful outcome but suggests the embryo is well-positioned for the next steps in your IVF journey.
