How does the IVF embryo grading chart work?

An IVF embryo grading chart answers the many questions that patients frequently ask their doctors about the different kinds of embryos and their likelihood for implantation.

An embryologist studies lab-created embryos under a microscope and grades them based on appearance during the in vitro fertilization process.

To maximize the likelihood of a successful pregnancy, embryologists and fertility doctors use the grading system to help them choose the most viable embryos for uterine transfer.

Embryo grading usually requires evaluating different characteristics of the embryo as:

1. Cell number: The embryo’s cell count is determined. Ideally, at particular stages of development, embryos should attain a given number of cells.
2. Symmetry: The symmetry and homogeneity of the cells are evaluated and a high degree of symmetry is a good sign.
3. Fragmentation: The presence of tiny, asymmetrical cell fragments in the embryo. Higher-quality embryos have fewer fragments.
4. Blastomere equality: This checks if the cells are equally divided
5. Blastocyst formation (if applicable): At a later developmental stage, when the embryo forms a blastocyst, assessment of the inner cell mass (ICM) and trophectoderm (TE) may be part of the grading process.

The embryo’s appearance under a microscope is the only factor used to determine this grade. Although it provides a reasonable indication of which embryos have a better chance of surviving, the lack of information regarding the embryo’s genetic makeup keeps it from providing solid proof that the embryo is of the ‘baby-making’ sort.

Embryo grading at day 3 is done on the following three criteria:

1. The number of cells in the embryo: A good-quality, normally-growing, embryo on day 3 would typically have 6-10 cells held within an outer shell called the Zona Pellucida (ZP). Research (1) shows that embryos with 8 cells or more are most likely to develop into a healthy blastocyst. Different clinics grade embryos upto 4 or 5 points, with 5 being the lowest.
2. Fragmentation: Embryos with no or little fragmentation are labeled grade A, those with more than 10% fragmentation are grade B, and the ones with more than 25% and 50% fragmentation are labeled C and D grade respectively. Embryos with grade A and B are considered good and most likely to result in a healthy pregnancy.
3. The appearance of cells under a microscope: Embryos with cells of equal sizes and no fragmentation are considered grade 1 or the best quality. Some laboratories label embryos as:
4. G (good) — all cells are equal size
5. F (fair) — a few of the cells are different sizes
6. P (poor) — cells are mostly all different sizes

An embryo with label 8AG will be considered the best.

The three parameters of embryo grading on Day 5

Number: Based on the expansion of blastocyst

The expansion of a blastocyst gives an indication of its ability to develop and grow. An embryo that does not expand, will not be able to grow.

First letter: Grade of the inner cell mass (ICM), which will form the fetus

Second letter: Grade of the trophectoderm (TE), which forms the placenta and other supporting cells

In a very early blastocyst, the cavity is just starting to form and the cells cannot yet be differentiated into the two types. An expanded blastocyst has a well-defined cavity, around 100-125 cells all covered with a thin ZP. The hatched blastocyst has over 150 cells with the embryo bursting out of the shell.

Well-developed blastocysts with healthy contents are obviously better for successful pregnancies. According to research, higher graded blastocysts (e.g. 3AA) were found to result in higher pregnancy rates at around 65%. Blastocysts that were graded average (like 2AB, 2BA, 4AC) had about 50% pregnancy rates and poor quality blastocysts (such as 4CC, 2BB, 3BC, 4CB) resulted in pregnancy rates of only 33%.

However, there’s nothing like best embryo grading for transfer as we cannot determine the exact usability of an embryo simply by looking at a grading chart.

An embryo with 1CA grade might seem poor at first, but it may still be developing and might turn into grade 4AA within a day.