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What does an embryo grading mean?

In a surrogacy process you want everyone around you to be focused on maximizing your chances of a successful embryo implantation and pregnancy, and a healthy birth, with as few attempts as possible. One of the parameters that help for a successful transfer is the embryo grading.

The embryos that are frozen before they are transferred to the surrogate are graded according to a visual assessment where an embryologist in a lab determines the quality of the embryo. By using embryos with a higher grading we are helping to maximize our chances of success.

Although the embryo grading system is old, the final grading can change even among embryologists and between the embryo’s stages of development since it is a subjective visual assessment.

With surrogacy, we mainly deal with blastocyst embryos, meaning ones that have reached day five or six of development since fertilization. The embryo’s overall degree of development at this stage is defined on a 1-6 scale: The number indicates the day since fertilization. Day 5 or 6 blastocysts will be graded accordingly, meaning 5-6. At this stage of the embryo you can already decipher two separate groups of cells, ICM (from which the actual fetus develops from) and the trophectoderm cells (that define its external structure). Each of the cell groups is graded separately on a descending scale from A-C according to the number of cells and the cohesion between them.

For example - An AA5 grading means that the embryo is in day 5 of development, where the two groups of cells have the highest grading - A.

Another example - An AB6 grading means that the embryo is in day 6 of development, where the ICM group has a high rating of A and the external structure cells are not quite as good and are graded B.

Good quality embryos will be transferred to the uterus or frozen for future use, while low quality embryos will stop developing at a certain stage.

Statistically, the higher the embryo’s grading, the better its chances of developing into a healthy pregnancy and birth.

Embryos that have undergone advanced tests like PGS or PGT-A and have been found “normal” will usually have the highest gradings, since the test is not only visual.

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