40w LaterGuide

During IVF, it is natural to pay close attention to your embryo grades. However, a lower grade does not mean that implantation cannot occur, and even a highly graded embryo does not guarantee pregnancy.

Embryo grading is a way of assessing an embryo’s development and appearance to help determine which embryos may be prioritized for transfer or freezing.

How are embryos evaluated?

Assessment methods can vary depending on the developmental stage and the laboratory. Embryologists generally look at how the embryo is developing, the number, size and appearance of its cells, and features such as fragmentation or multinucleation.

At the blastocyst stage, the degree of expansion and the appearance of the inner cell mass and trophectoderm are also evaluated.

1. Embryo development

After fertilization, an embryo develops through repeated cell divisions. Around Day 2, a 4-cell embryo may be considered to be developing appropriately, while around Day 3, an embryo may have about 8 cells. However, embryos do not all develop at exactly the same rate, and cell number alone does not determine embryo potential.

Some laboratories use time-lapse technology to continuously observe embryo development inside the incubator. While this provides additional information about development, using time-lapse technology does not necessarily improve the chance of pregnancy or live birth.

2. Cell appearance and symmetry

For cleavage-stage embryos, embryologists assess not only the number of cells but also their size, shape and pattern of division. Relatively even cell division is one of the features considered during morphological assessment.

3. Fragmentation

Fragmentation refers to small pieces of cytoplasm that can appear between cells as an embryo divides. The amount of fragmentation is one of the characteristics assessed in cleavage-stage embryos, and embryos with less fragmentation may generally be prioritized.

However, the presence of fragmentation does not mean that implantation or pregnancy is impossible.

4. Multinucleation

Multinucleation means that more than one nucleus is seen within a single blastomere. It is another feature considered when assessing cleavage-stage embryos, but it is evaluated together with the embryo’s other characteristics rather than being used alone to decide whether an embryo can be used.

How are Day 3 embryos graded?

Cleavage-stage embryos are assessed using features such as the number and size of cells, cell symmetry, fragmentation and multinucleation.

For example, an embryo with around 8 cells on Day 3, little fragmentation and one nucleus per cell may be prioritized. However, embryos that do not fit these characteristics perfectly can still continue to develop and result in pregnancy.

How are Day 5 embryos graded?

Once an embryo develops into a blastocyst around Day 5 or 6, a different grading approach is used.

In the widely used Gardner system, the blastocyst’s stage of expansion is assessed along with the inner cell mass (ICM) and trophectoderm (TE). This produces grades such as 4AA, 4AB or 3BB.

The number represents the blastocyst’s stage of development and expansion, while the two letters describe the appearance of the ICM and TE. Grading systems and terminology can vary between laboratories.

Does a higher grade mean a better chance of pregnancy?

Embryos with more favorable morphological features tend, on average, to have greater implantation potential, which is why grading can help determine the order in which embryos are used.

However, an embryo grade is not a guarantee of pregnancy. A highly graded embryo may not implant, while a lower-graded embryo may implant and result in a healthy birth.

Rather than directly comparing your embryo grade with someone else’s, it is best to understand it in the context of the embryo’s developmental stage and your individual treatment.