Patient guide
Embryo Grading vs. Genetic Testing
Reticular Editorial Team
Patient Education
The same embryo can come back with two results. One says 4AA. The other says euploid. A different embryo might pair a modest 3BB with an aneuploid result. The two can seem to compete, as if one has to be the "real" grade.
They are not competing. They answer two different questions about the same embryo. It helps to take them one at a time before you put them side by side.
There are two separate things being measured. One is how the embryo looks as it grows. The other is what a few sampled cells tell the genetics lab. An embryo can score high on one and low on the other, which is exactly why the two results do not always agree. The rest of this article walks through each one on its own, then puts them side by side so the cases where they disagree make more sense.
Grading: how the embryo looks as it grows
Embryo grading is done by the embryology team, and it is essentially a visual and developmental assessment. At the blastocyst stage, many labs use a Gardner-style system that looks at three main features: how expanded the blastocyst is, how the inner cell mass appears, and how the trophectoderm appears. That is where a code like 4AA comes from: a number for expansion, then two letters for those two cell groups.
The inner cell mass is the group of cells expected to contribute to the fetus. The trophectoderm is the outer layer expected to contribute to the placenta. ASRM's embryo grading materials describe these commonly used grading features, including Gardner-style expansion and cell-quality categories (ASRM grading scales).
A higher grade often means the embryo looked more expanded or organized at the moment it was checked. That information can help a lab decide which embryos are suitable for biopsy, freezing, or transfer.
But grade is a description, not a verdict. It is partly subjective. Two embryologists can score the same embryo a little differently, lab practices vary, and lower-graded embryos can still have real reproductive potential. The grade tells you how the embryo looked. It does not, by itself, say anything about chromosomes.
Genetics: what the sampled cells show
The second result comes from preimplantation genetic testing, or PGT, which usually involves removing a small number of cells from an embryo and sending those cells to a genetics laboratory. The grade looks at the whole embryo under a microscope; genetics looks only at the few cells that were sampled and asks one specific question of them. SART describes PGT as testing in which cells are removed from an embryo and screened for genetic abnormalities, with categories such as PGT-A, PGT-M, and PGT-SR (SART glossary).
PGT-A
Chromosome number
Asks whether the sampled cells appear to have the expected number of chromosomes.
PGT-M
A known family variant
Asks whether the embryo appears to have inherited a specific variant already identified in the family.
PGT-SR
A chromosome rearrangement
Used when a parent carries a rearrangement that could lead to missing or extra chromosome material in embryos.
For PGT-A, especially, cautious wording matters. ASRM notes that PGT-A use has grown, but that its value as routine screening for all IVF patients has not been demonstrated. SART also emphasizes that PGT-A is a screening test and does not guarantee an ongoing pregnancy or live birth (ASRM 2024 committee opinion, SART FAQ).
Putting grade and genetics side by side
Here is where grade and genetics come together. Because they are measured separately, every embryo falls into one of four boxes. Two boxes are the expected ones, where grade and genetics point the same way. The other two are the surprises, where a strong-looking embryo tests abnormal or a modest-looking one tests euploid. Those two boxes are the main reason it helps to compare grade and genetics at all.
| Euploid (expected chromosome number) | Aneuploid (missing or extra chromosomes) | |
|---|---|---|
| Looks strong high grade |
Grade and genetics agree — the combination most people picture by default. | The hard surprise. A great-looking embryo can still test aneuploid; appearance cannot see chromosome count. |
| Looks modest lower grade |
The reassuring surprise. A modest-looking embryo can test euploid; a lower grade is not a chromosome problem, and it can still be considered for transfer. | Grade and genetics agree the other way. |
Those two off-diagonal cases — a strong-looking embryo that tests aneuploid, and a modest-looking one that tests euploid — are why grade and genetics are not the same thing.
Grade on its own does not decide whether an embryo becomes a healthy baby. A lower-graded euploid embryo can lead to a perfectly healthy pregnancy. But most full aneuploidies are unlikely to result in an ongoing, healthy pregnancy, which is why a chromosome finding usually carries more weight than appearance when the two disagree.
If an embryo lands in one of those off-diagonal boxes, it does not mean either test failed. It means the embryo carries two kinds of information that do not have to match. The helpful question is not, "Which result should I ignore?" It is, "How does this clinic weigh these results for embryos like mine?" Policies can differ, especially for mosaic results, no-result embryos, day 7 embryos, or embryos with lower morphology grades.
How clinics weigh grade and genetics together
Even when embryos are genetically tested, grade still matters. Embryos first need to grow to a stage where the lab believes biopsy and freezing are appropriate, and that judgment leans on grade. After results return, the care team may consider the genetic result, embryo grade, day of blastocyst development, medical history, and patient priorities all at once.
| Question | What helps answer it? |
|---|---|
| Did the embryo look developmentally ready for biopsy, freezing, or transfer? | Embryo grade and day of development |
| Did the sampled cells appear to have the expected chromosome number? | PGT-A result |
| Was a known family variant or chromosome rearrangement part of the plan? | PGT-M or PGT-SR result, if ordered |
| What else could affect the chance of pregnancy? | Age, uterus, medical history, embryo cohort, lab factors, and other clinical context |
This is why many clinic conversations sound layered. A clinician may talk about a euploid embryo with a lower grade, or a high-grade embryo that is not recommended for transfer because of a genetic result. Neither sentence is a contradiction. It means the team is reading both the grade and the genetics at once and deciding which one carries more weight for this specific embryo.
A few questions worth asking
- How does this lab assign embryo grades, and how consistent is grading between embryologists?
- After PGT results are available, how much weight does embryo grade still carry?
- What result categories can this PGT lab report, such as mosaic, segmental, inconclusive, or no result?
- Would your recommendation change if we have one embryo, several embryos, recurrent pregnancy loss, advanced maternal age, or a known familial variant?
What grade and genetics each add
It is tempting to ask which result is the "real" one. But grade and genetics were never meant to give the same answer, so picking a winner does not help.
A more useful question is: for this embryo and this decision, what does each one actually add? Grade tells you how the embryo developed and whether the lab considered it ready for the next step. Genetics tells you the answer to the specific question that was ordered of the sampled cells. Together, they describe an embryo more fully than either could alone. Neither one promises a pregnancy, a live birth, or a child without health conditions.
One practical note: Reticular's report does not include embryo grade (morphology) by default. It focuses on the genetic layer. If grade matters to your decision, you can adjust your priorities and share the grading information so it is factored in.