IVF is a complex procedure involving a series of complicated procedures. Among them, embryo transfer is the final procedure that determines the success of the IVF cycle.
Embryo transfer is when one or two embryos are chosen and transferred into the uterus to implant in the uterine lining. Successful implantation results in pregnancy.
Embryologists usually fertilize at least five or six embryos during a cycle. The best one among these embryos is then chosen for embryo transfer.
But how do embryologists decide which embryo is best and which is not? This is made possible through embryo grading. In this article, let’s look at what embryo grading is and the role it plays in successful implantation and pregnancy.
What is Embryo Grading?
Embryologists use embryo grading to get a clear idea of which embryos to use, how many to use, and when to carry out the embryo transfer.
This is crucial for finding the best possible embryos to be transferred at the best possible time. Once egg retrieval is finished, a developed embryo is transferred on Day 3 or Day 5. Making an informed choice is easier when you understand how the days differ.
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Different Embryo Grading Systems
Embryo transfer usually occurs on day 3 (cleavage stage) or day 5 (blastocyst stage) of egg retrieval. Doctors usually prefer day 5 transfer. But, if the embryo develops well, it can also be transferred on day 3.
Since the stage of development will be different on day 3 and day 5 embryos, they have different grading systems.
Day 3 Embryos
Day 3 embryos are also called “cleavage embryos” because this is when their cells start “cleaving” (dividing), but they don’t grow in size. The genetic material in the embryos replicates, and cells divide without changing the volume of the embryos.
Day 3 embryos have about 6–8 cells. Embryologists use the number of cells and degree of fragmentation to assess and grade these embryos. Day 3 embryos are graded into Grades A, B, and C.
The embryo with the highest number of evenly sized cells with very little fragmentation is considered to be of the highest grade.
Grade A – The embryos have 6–8 evenly sized cells with no or less than 10% fragmentation.
Grade B – The embryos have unevenly shaped cells with 25–50% fragmentation.
Grade C – The embryos have more than 50% fragmentation.
Day 5 Embryos
Day 5 embryos are also called “blastocyst embryos.” Most embryologists believe that the grading done during this stage is more standard and gives the best results.
During this stage, the cells start multiplying faster. The embryo also starts increasing in size to accommodate the growing number of cells. The zona pellucida (outer shell) of the embryo starts thinning as it gets ready to implant in the uterus.
The cell division is divided into two groups:
- Inner Cell Mass (ICM). This group of cells multiplies to become the fetus.
- Trophectoderm Epithelium (TE). This group of cells develops into the placenta and other tissues the body needs during pregnancy.
You should know that day 5 grading is more complex than day 3 grading and depends on various factors. Each fertility centre might follow different protocols while grading its day 5 embryos.
Below are some aspects that embryologists look for while grading these embryos. This is also called the Gardener Blastocyst Grading System.
- The extent of the blastocyst's growth. Here, the blastocoel of the embryo is being measured. A blastocoel is a fluid-filled chamber that develops inside the embryo. They are measured in grades 1 through 6, with 6 being the highest standard. (Some centers measure them in grades 1 to 5.)
- The quality of the ICM. The ICM is responsible for developing the fetus. Here, grades run from A to C, with A being the highest standard.
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The quality of the TE. The TE creates the placenta and other tissues that develop during pregnancy. The grades are from A to C, with A being the highest standard.
- The extent of the blastocyst's growth. Here, the blastocoel of the embryo is being measured. A blastocoel is a fluid-filled chamber that develops inside the embryo. They are measured in grades 1 through 6, with 6 being the highest standard. (Some centers measure them in grades 1 to 5.)
- The quality of the ICM. The ICM is responsible for developing the fetus. Here, grades run from A to C, with A being the highest standard.
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The quality of the TE. The TE creates the placenta and other tissues that develop during pregnancy. The grades are from A to C, with A being the highest standard.
So, according to the Gardner blastocyst grading system, an embryo with the grade 6AA will be the one with the highest quality.
Embryo Grading and Success Rates
The grading system allows embryologists to choose the best embryo for transfer. Comparing day 3 and day 5 grades also lets them compare the embryo’s development.
Some studies show that embryos with the highest grades have a higher chance of pregnancy than embryos of lower grades. While this is true, it does not apply to all cases.
One should know that grading is not always the ultimate deciding factor for choosing the best embryo. In some cases, the embryo with the highest rate may fail, while the embryo with mediocre grades succeeds in implantation.
Conclusion
Embryo is one of the important factors that can determine your IVF cycle’s success. But remember that it is only one of the many factors.
Other factors like your health, food habits, and lifestyle also play a role in having a successful pregnancy. Talk with your fertility doctor and get a detailed plan that you should follow during your cycle to maximize your chances of success.
FAQs
Embryo grading allows embryologists to assess and identify the embryo with the highest chance of success. They do it by analyzing the development and quality of the embryo.
They are graded according to the stage of their development and how likely they are to implant in the uterus.
No, even though the embryo grading allows embryologists to choose the best embryo among all, it doesn’t always guarantee pregnancy.
There are some cases where the embryos with the highest grade failed, and the ones with mediocre grades succeeded in pregnancy.
No, embryo grading will not necessarily affect the success rate of the IVF cycle. However, it can help embryologists understand which embryo can potentially result in pregnancy.
