Addressing Common Embryo Grading Myths

Embryo grading is the evaluation of an embryo’s structural quality, which is one of several key components of success in in-vitro fertilization (IVF).

During the embryo grading process, a researcher known as an embryologist uses a microscope to carefully assess the development, cell structure, and growth rate of embryos, which are the fertilized eggs created during IVF. The higher the grade, the better the overall structural quality and, potentially, the greater likelihood of pregnancy.

While it can provide important information, embryo grading is not a guarantee of a healthy pregnancy.

Embryo grading is based on the Gardner system, a widely-used standard in fertility medicine. This system assesses three key structural components of day five blastocysts:

• Expansion (scale of 1-6)
• Inner cell mass quality (scale of A-C)
• Trophectoderm quality (scale of A-C).

Using the Gardner system, high-grade embryos are generally labeled 4AA, 5AA, or 6AA. Low grades are those that rank at a four or below on expansion and appear as B or C in terms of inner cell mass quality and/or trophectoderm quality.

Embryo grading is a visual assessment, and is performed by embryologists trained to spot subtle differences but who may vary in their interpretations. It should be just one of several considerations when deciding whether or not to implant an embryo.

We’re setting the record straight on five must-know embryo grading myths vs. facts.

Myth #1: A Higher Grade Guarantees Success

The notion that AA embryos guarantee success is misleading. The notion that AA embryos guarantee success is misleading. According to a 2021 peer-reviewed study published in the Journal of Assisted Reproduction and Genetics analyzing 927 single frozen embryo transfers, AA-grade blastocysts achieved live birth rates of 41.4%, BB-grade embryos 31.1%, and CC-grade embryos 13.3%.

These findings align with a 2023 Frontiers in Endocrinology analysis of blastocyst quality showing good-grade embryos at 44.4% live birth versus 30.2% for low-grade. Success depends on maternal age, uterine conditions, and other factors beyond grade alone. Lower-grade embryos like BB and even CC can (and frequently do) result in healthy pregnancies and shouldn’t be automatically ruled out.

Myth #2: PGT-A Testing Eliminates the Need for Grading

Research supports PGT-A testing in addition to embryo grading, not in place of it.

A 2024 Human Reproduction study found that even among euploid embryos, clinical pregnancy rates were 56.6% for better morphology versus 40.1% for poorer grades. PGT-A assesses chromosomes, while grading evaluates visual development. Combining both provides a more comprehensive assessment than either alone.

Myth #3: All Clinics Grade Embryos the Same Way

Many fertility clinics use the Gardner system, but they don’t all implement it in the same way.

The standards of the Gardner system are not uniform, nor are the methods used in the evaluation process. Some clinics add refinements, focus on different day grades, or interpret more strictly, resulting in varying degrees of result accuracy and comparability. Variability also stems from human factors such as experience and equipment.

For a better comparison, focus on clinic success rates rather than inter-clinic grade comparisons.

Myth #4: Poor-Grade Embryos Should Never Be Transferred

Low-grade embryos are often dismissed, yet evidence shows their potential. In fact, even C-grade embryos may result in a successful pregnancy, though their rates are generally lower.

We recommend that transfer decisions be made holistically, with full consideration of a patient’s history and health conditions. These combined factors give a much better picture of viability and help prevent the automatic rejection of low-grade embryos.

Myth #5: Time-Lapse Monitoring & AI Mean No More Grading Subjectivity

Time-lapse monitoring and AI are two amazing advancements in embryo grading. But they’re not the end-all, be-all, and certainly can’t erase all subjectivity in the process.

The real benefit of these tools comes in their ability to identify patterns and enhance decision-making accuracy. For example, EmbryoScope’s images create detailed “movies” that make clear patterns invisible in spot checks. AI flags them, and the embryologist has another data point. Still, human interpretation remains crucial, with many subjective elements still at play.

As we separate embryo grading facts from myths, it’s important to keep an eye on the big picture, namely, what you realistically can and cannot learn from embryo grading.

At its core, embryo grading provides probabilities, not guarantees. Success hinges on other influences too, including genetic health and uterine conditions, and even lower-grade embryos frequently lead to healthy pregnancies. This nuance challenges some of the most persistent embryo grading myths, most of which tend to lean toward black-and-white thinking.

Success rates with embryo grading are correlative rather than strictly causative, so you’ll find cases where AA embryos don’t implant despite their promising appearance and where lower-grade ones thrive against expectations. That’s because factors such as hormonal support and precise transfer techniques often carry more weight than visual grading alone.

Countless “imperfect” embryos have gone on to create perfect families. Pair embryo testing with other tests like PGT-A and talk to your specialist about their single embryo transfer philosophy and wider approach to assessing embryo quality.