Embryo Grading

What Embryo Grading Describes

On day 3 after fertilization, an embryo is at the cleavage stage, made up of a small number of individual cells. Labs describe it with three things: how many cells it has, how even those cells are in size (symmetry), and how much fragmentation is present, meaning small bits of cellular debris outside the main cells.^[1] A day-3 grade is a shorthand for that combination, not a single score.

By day 5, an embryo that has kept developing reaches the blastocyst stage, and labs often describe it with the Gardner system.^[2] A Gardner grade has a number from 1 to 6 for how expanded and hatched the blastocyst is, followed by two letters, each usually A, B, or C. The first letter grades the inner cell mass (ICM), the cluster of cells that goes on to become the fetus. The second letter grades the trophectoderm (TE), the outer layer of cells that goes on to become the placenta.^[2] So a grade like 4AB reads as: expansion stage 4, ICM grade A, trophectoderm grade B. It's a description of appearance at that moment, not a ranking of the embryo against others.

Grading systems vary between labs. An international group of embryologists published consensus criteria because different clinics were using different scales and definitions.^[1]

Why People Track It

The grade shows up as one line in the lab's report during an IVF cycle, alongside other values like estradiol, hCG, and cycle-day notes. It's a descriptive part of what the embryology lab records at each check-in, not something meant to be interpreted on its own. The clinic and embryology lab reading the whole picture are the ones drawing conclusions from it.

For more on the other lab values that show up during an IVF cycle, see the best IVF tracking app for logging clinic data.

How Go Go Gaia Tracks It

Embryo grades come from your clinic, not from an app. Go Go Gaia lets you log the grades your clinic reports with a single tap and charts them on your IVF timeline next to lab values like estradiol and hCG and your cycle data, so the whole cycle stays in one place instead of scattered across portal messages and paper printouts.

What the Research Shows

Grading is a morphology assessment: it describes what the embryo looks like under a microscope at one moment, not its genetics or long-term potential. A multicenter study asked embryologists to grade the same set of day-5 embryos and found only fair-to-moderate agreement on the morphology grades themselves, between different embryologists and even when the same embryologist graded the same embryo twice.^[3] Two people looking at the same embryo can land on different grades.

The original study describing the Gardner system found that blastocyst score was associated with implantation and pregnancy rates across the patients studied.^[2] A 2025 review pooling close to 43,000 embryos across 33 studies found similar population-level associations between morphology grade and live birth rates.^[4] Both are patterns across large groups. Neither predicts a single embryo's outcome: embryos with lower grades have gone on to healthy births, and a top grade is not a guarantee.

Related Terms

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

What do the letters in a blastocyst grade mean?

In the Gardner system, a blastocyst grade like 4AB has a number for how expanded the blastocyst is (1 to 6) followed by two letters. The first letter (A, B, or C) grades the inner cell mass, the cluster of cells that becomes the fetus. The second letter grades the trophectoderm, the outer layer of cells that becomes the placenta.

Do all clinics grade embryos the same way?

No. Labs can use different grading scales and different criteria for what counts as each grade, which is why an international group of embryologists published consensus criteria to make reporting more standardized. Even under a shared system, embryologists can grade the same embryo differently, so a grade only means something in the context of the lab that assigned it.

Does a lower grade mean an embryo won't work?

No. Grade-to-outcome associations are population-level patterns seen across large groups of embryos, not a prognosis for any one embryo. Embryos with lower grades have resulted in healthy pregnancies, and a top grade is not a guarantee. Grading is one input the clinic and embryology lab weigh, not a stand-alone prediction.