There are 3 primary qualities the embryologist will be looking at in assessing the embryo. The blastocyst will first be assigned a number between 1-6 based on expansion. Grade 1 means the blastocyst cavity is under half the volume of the embryo, while Grade 6 means the embryo has completely hatched, indicating higher chances of success. Next come the letters. The first letter, A, B or C, refers to the inner cell mass (ICM) and dictates how solid or freely the cells are packed. The second letter, representing the trophectoderm epithelium (TE) grade, is also measured as A, B or C, with Grade A referring to a solid layer of cells and Grade C meaning few cells. Just like in school, an A is best.
The role of the embryologist
Once the retrieved embryos have been assigned a grade, the embryologist will determine which embryo should be transferred. In addition to looking at variables such as ICM and TE, the fertility specialist will also consider the patient’s age, underlying fertility diagnosis, and medical history in making a determination. In some cases, if all the embryos have a low grade, the decision will be made to transfer 2 or more, increasing the chances that one will be successful. However, this approach also runs the risk of twins, which can make pregnancy more high-risk.
Day 3 vs Day 5
Embryos grow rapidly, changing from just 4-8 cells on Day 3 to 70-100 cells by Day 5. Embryo grading can be performed as early as Day 3. If an ideal embryo is identified, a transfer can occur at this stage. Some research suggests that good day 3 embryso are more likely to result in pregnancy since transfer into the uterine environment provides a more hospitable environment than a lab dish. On the other hand, if all embryos appear to be developing equally, the embryologist may want to wait until Day 5 to see if a clear winner emerges. With more cells present, grading can take place again, and the best embryo can be identified and transferred.
Choosing the best embryo
When undergoing IVF, the ability to closely monitor the developing embryo and select the best option for transfer can increase the chances of a successful cycle. With a grade in hand, the embryologist and fertility team can work together to make a personalized plan for transfer. If all goes according to plan, the science of embryo grading can lead to a healthy, happy baby.