What is Embryo Grading in IVF?
The quality of the embryo is the single most important factor that can determine the success or failure of embryo transfer. And thus, to ascertain the quality of the embryo – reproductive medicine specialists have devised an embryo grading system to determine which embryos have the best appearance, and thereby the best possible chance of resulting in a successful embryo transfer.
However, one must also understand that numerous factors determine the quality of the embryo that are outside the purview of being able to be deduced just by looking at it through a microscope.
Thus, embryo grading is essentially a tool that must be used in context with a patient’s age, patient history, and various other information to determine the optimal day of transfer, the number of embryos required to be transferred, and of course, exactly which embryos to transfer. All of these are critical decisions that help mitigate risks and increase the chances of success.
It is now a common practice to have a different scale for day 3 and day 5 embryo transfers. This is because of the fact that there is a significant developmental variation of the embryos on each of these days. Based on the grading, it is then decided which of the embryos can be transferred and which can be frozen for later use.
Day 3 Grading System
Referred to as the cleavage stage embryos, at this stage the embryo is not growing in size, but the cells are getting divided within themselves. This is where the terminology – cleavage-stage embryo transfer comes about. Here, the genetic material replicates itself and the cells are dividing but the overall size of the embryo stays just the same.
For grading cell 3 embryos, the experts are concerned about the cell morphology and are looking to determine the number of cells and their appearance. On day three, anywhere between 6 to 10 cells is agreed as a good number and ideally, it must be eight. The fact that cells do not divide synchronously is the reason for such variation. Also, it is not a given that cells will always follow the rule, and, in many cases, it may be seen that embryos will have 3 or 5 cells as well. This does not automatically rule out these embryos as bad ones.
While cell number is an objective quantity, the second parameter – cell appearance is a little more subjective. Graded on a scale of 1 to 4, cell appearances, experts use specific criteria to determine the appearance of the embryos. Grade 1 embryos will have cells of equal size and there is no fragmentation between them. Grade 2 embryos also have cells of equal size but might evidence some form of fragmentation.
There is a grade 2.5 wherein most cells are of equal size, there is also a moderate amount of fragmentation, while grade 3 embryos will be those with an unequal number of cells and moderate fragmentation. Finally, the grade 4 embryos will be those with equal or unequal size and moderate to heavy fragmentation.
Day 5 Grading System
Between day 3 and day 5 the embryos will move from the cleavage stage to the blastocyst stage. The cells are now of two varieties – baby-making ones, and the placenta-forming ones. In many cases, doctors prefer waiting up to the 5th day before the embryo transfer – there are several advantages associated with it. By day 5, the embryo is growing up quickly. From just division, the embryo is now actually growing – and thus, the grading system is a little more complex when compared to day 3.
Both the placenta and fetus are equally important for the success of the embryo transfer and therefore both must be ascertained. There is an alphanumeric grading system that is followed for grading the day 5 embryos.
- Gradation on a scale of 2 to 6 – this determines the expansion of the cavity. 2 being the smallest and 6 being the largest
- Graded on a scale of A to C – this determines the appearance of the fetus making cell mass. A being the best and C the least.
- Graded on a scale of A to C – is also the appearance of the placenta making cells. A being the best and C the least.
2 – cavity takes 1/3rd of the embryo
3 – cavity takes 70% of the embryo
4 – cavity takes almost 100% of the embryo
5 – embryo expansion complete and splitting open from the zona
6 – embryo expansion complete and hatched from the zona
A – well-defined cells
B – not too well-defined cells
C – darker cells, the appearance of degeneration
Placenta Cell Grading
A – even layer, equal size, and smooth cells
B – irregular and grainy cells
C – extreme irregularity and graining of cells.