Embryo grading is a crucial tool that helps embryologists and physicians during an IVF treatment to assess the quality of an embryo so as to determine, the optimum embryo/(s) to transfer, the day of transfer and the appropriate number of embryos to transfer. Typically done on Day 3 and Day 5, grading is not used independently, but is just one part of a complex process that is used along with many factors like patient’s age, fertility history, and other information for deciding the optimum embryo(s) to transfer to maximize the chances of successful pregnancy and minimizing the risks multiple pregnancies.
At GENESIS, all assessments are done on powerful inverted microscopes. The grading process evaluates embryos based on the “appearance of the embryo” and its developmental progress, helping the embryologist to decide which embryo to transfer, freeze or to discard.
It relies heavily on the subjective judgment of embryologists, which can vary between individuals and clinics. To minimize that GENESIS participates in a CAP proficiency testing program 3 times a year to verify accurate and standardized embryo quality assessment.
While embryo grading provides valuable and critical information, it is not an exact science. The appearance of an embryo does not always correlate perfectly with its genetic health or its ability to result in a successful pregnancy. It is important to note that even lower-graded embryos can sometimes result in successful pregnancies. Additionally, grading does not guarantee pregnancy outcomes, as other factors such as uterine receptivity and genetic abnormalities can also influence success
Comprehensive genetic testing (such as preimplantation genetic testing for aneuploidy, or PGT-A) can provide additional insights into an embryo’s viability.
Day 3 Embryos
Day 3 (D3) embryos are referred to as “cleavage stage embryos”. This means they are dividing (or cleaving) but the embryo itself is not growing in size. They typically consist of 6-8 cells inside an outer covering called the zona pellucida; also known as the shell. GENESIS uses cell number and degree of fragmentation to assess the quality of D3 embryos. Typically, a higher number of cells with lower fragmentation is considered more favorable, for e.g. 8A on D3 is the best grade. Fragmentation refers to presence of small debris of cellular material that are not part of the intact cells. The symmetry of the cells (blastomeres) in a high-quality embryo should be of equal size and shape and is taken into consideration. Asymmetrical embryos might have a reduced potential for implantation.
Grade A
These embryos show that there are 6-8 evenly sized cells, with no or less than 10% fragmentation.
Grade B
These embryos have more uneven or irregularly shaped cells with 25-50% fragmentation.
Grade C
These embryos show 50% or more fragmentation.
Grade A, Grade B, Grade C
Day 5 Embryos
Day 5 (D5) or blastocyst grading is more standard, as most clinics use the Gardner and Schoolcraft’s three part scoring system. By day 5 embryos should have started to outgrow the tight confines of the zona pellucida, or shell.
Blastocysts are graded on three factors:
1. Blastocyst Development:
Degree of expansion based on how expanded the cavity is. This is graded on a scale of 1-6 with 6 being the most expanded.
2. Inner Cell Mass (ICM):
Appearance of the inner cell mass (the part that makes a baby) which is graded for the compaction of cells with either an A, B, or C with A being the best.
A: Many cells, tightly packed.
B: Several cells, loosely grouped.
C: Few cells
3. Trophectoderm (TE):
Appearance of the trophectoderm (the part that makes the placenta) also graded for the number of cells with A, B or C; with A being the best.
A: Many cells, forming a cohesive layer.
B: Few cells, forming a loose layer.
C: Very few cells.
Each of those factors is combined to create the grade (number, letter, letter).
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Blastocyst Grade per factor
The first part of the grade is a number. The number represents the expansion of the embryo cavity.
- Blastocoel cavity is 1/3 the volume of the embryo
- Blastocoel cavity is 1/2 the volume of the embryo
- Full blastocyst is 80%, completely filling the embryo
- Expanded blastocyst, the cavity is larger than the embryo; the zona is thinning
- Expanded blastocyst, beginning to hatch out of the zona
- Expanded blastocyst, fully emerged from the zona
The second part of the grade is a letter. The first letter following the number represents the inner cell mass, or ICM quality.
A. Many cells, tightly packed
B. Several cells, loosely grouped
C. Very few cells
The third part of the grade is another letter. The second letter represents the quality of the trophectoderm. This is the cellular layer that makes the placenta and surrounding membranes.
A. Many cells, forming a cohesive epithelium
B. Few cells, forming a loose epithelium
C. Very few large cells
Typically, an expanded blastocyst with a well-developed ICM, which forms the fetus, and TE, which becomes the placenta, are indicators of a healthy embryo. For example, a 5AA on D5 is the best grade.
4AA
5AA
6AA
At Genesis, embryos exhibiting marked fragmentation and poor cellular integrity are categorized as MF (multifragmented).
These embryos are not given a standard morphological grade, as the extent of fragmentation renders grading unreliable and potentially misleading in representing their developmental potential.
How important is embryo grading?
Despite its limitations, it remains an important factor in improving chances of a successful pregnancy.
To determine whether an embryo has good potential or not, all of the components of the embryo must be taken into account. While an A grade is better than a C grade, embryos continue to develop. Because of this, their grading can change; eventually making lower graded embryos candidates for embryo transfer or freezing.
Embryo grading is a tool to help scientists and physicians; but it is only one part of the decision process. This is why our physicians and scientists determine the potential of an embryo by taking into account not only the grading, but all of a patient’s unique medical history.
At GENESIS, our goal is to give our patients the highest chance of a successful pregnancy and a healthy baby. Learn more about how Genetic Screening and Single Embryo Transfer can help.
The future of embryo grading
Artificial Intelligence (AI) has the potential to change many aspects of healthcare, and embryo grading in IVF is no exception. The integration of AI into embryo grading holds significant promise for improving the accuracy, consistency, and outcomes of IVF treatments
As mentioned earlier traditional embryo grading relies heavily on individual and subjective judgment of embryologists. AI systems can analyze embryos using standardized criteria, reducing variability and increasing objectivity. The integration of AI into embryo grading promises to enhance the accuracy, consistency, and efficiency, and has the potential to learn to identify subtle features and patterns that correlate with successful pregnancies. This enables more precise grading than human eyes alone can achieve.
While AI can enhance embryo grading, human expertise remains indispensable. Embryologists will continue to play a critical role in interpreting AI-generated insights and making final decisions.
At GENESIS, we are committed to explore new technologies that can improve patient care. Therefore, AI in embryo grading is certainly in the books.
Stay tuned.
Ref: Davis Gardner, Colorado Center for Reproductive Medicine
Frequently Asked Questions About Embryo Grading
What is embryo grading in IVF?
Embryo grading is a morphological assessment used in IVF to evaluate embryo quality based on its appearance under the microscope. Embryologists assess developmental stage, cell organization, symmetry, and degree of fragmentation to help identify embryos with higher implantation potential.
What do embryo grades like 4AA or 3BB mean?
Embryo grades consist of a number and two letters. The number reflects the degree of blastocyst expansion, while the first letter describes the quality of the inner cell mass (which forms the fetus) and the second letter describes the trophectoderm (which forms the placenta).
Does embryo grading predict IVF success?
No, embryo grading does not guarantee pregnancy success with certainty. It serves as a useful selection tool, but it is not definitive. High-grade embryos may not implant, while embryos with lower grades can still result in healthy pregnancies.
What is considered a good embryo grade?
Embryos graded AA or AB are generally considered high quality. However, embryos with B grades are good quality —and in some cases even C grades—can still be viable and result in successful pregnancies. Embryo grading should be interpreted as a continuum rather than a binary classification.
How are embryos graded at different stages?
Grading criteria vary by developmental stage. On day 3 (cleavage stage), assessment focuses on cell number, symmetry, and fragmentation. By day 5 or 6 (blastocyst stage), grading evaluates the degree of expansion as well as the quality of the inner cell mass and trophectoderm.
What is the difference between inner cell mass and trophectoderm?
The inner cell mass develops into the fetus, while the trophectoderm gives rise to the placenta and supporting structures. Both components are graded independently, as each plays a critical role in implantation and ongoing pregnancy.
Can lower-grade embryos still result in pregnancy?
Yes, lower-grade embryos can still result in successful pregnancies. Morphological grading reflects appearance, not genetic competence, and therefore does not fully determine implantation potential.
Why is embryo grading considered subjective?
Embryo grading is inherently subjective because it relies on visual interpretation. Although standardized criteria exist, there can be variability between embryologists and laboratories based on experience, training, and grading systems.
What role does genetic testing play compared to embryo grading?
Genetic testing (such as PGT-A) evaluates the chromosomal status of an embryo, whereas grading assesses morphology. These approaches provide complementary information—morphology reflects structural development, while genetic testing offers insight into chromosomal normalcy.
How do doctors use embryo grading during IVF?
Embryo grading is used alongside other clinical factors—such as patient age, medical history, and genetic testing results—to guide decisions about embryo transfer and cryopreservation. It is one component of a broader, individualized treatment strategy.
Why are some embryos labeled MF instead of being given a grade at Genesis?
At Genesis, embryos with severe fragmentation are categorized as MF rather than assigned a conventional grade. In such cases, the degree of fragmentation limits reliable assessment of key morphological features, and assigning a standard grade may not accurately represent the embryo’s developmental potential.
This information has been medically reviewed by Alka Goyal, PhD, the Director of Laboratories at Genesis Fertility
If you would like to learn more about GENESIS Fertility New York or are ready to schedule an appointment, please speak with one of our representatives at 929-605-5467.
