The embryo grading system allows us to classify embryos by taking into account aspects of the embryo and how it’s dividing, in order to perform embryo selection and select the best embryo for the moment of transfer, with the goal of increasing our success rates.
Additionally, embryos are often graded using specific scales, like the Gardner grading system, which takes into account both the embryo’s morphological features and the stage of development. This grading is crucial for maximizing the chances of a successful pregnancy.
An embryo quality grading system is a tool used in vitro fertilization (IVF) to evaluate and classify embryos based on their appearance and development during the initial days of cultivation. This classification helps fertility specialists select embryos with the highest potential for implantation and successful pregnancy development.
How is embryo quality assessed?
The evaluation of embryo quality is based on several criteria and grading systems, including:
1. Grading Based on Development Stage:
2. Morphological Aspects:
3. Grading System:
4. Continuous Observation:
5. Morphological Assessment:
6. Use of Advanced Technologies:
In conclusion: evaluating embryo quality is a crucial process in IVF that relies on a combination of morphological and developmental criteria. Grading systems help identify embryos with the highest potential for implantation and successful pregnancy development, allowing fertility specialists to make informed decisions about which embryos to transfer.
We have some options to monitor how the embryo is developing. Toxicity is actually when the embryo is under stress. When somebody is under stress, they are not performing well. The stress can be either from the abnormal embryo but also can be from an embryo that the environment is not friendly – the bad culture conditions. A problem that we don’t know. I don’t believe that we can make any embryo better from what we can but we can make embryos worse from what they could be. Nobody can improve an embryo, so I believe that having a good laboratory where you maintain the conditions very good for the embryo you have minimal chances of the external factors affecting the embryo and there is no point to test those things. I believe that the natural environment corrects everything, even if an embryo is somehow stressed outside by putting it back will recover. Only if we damage the embryo then it will show all of those things but this is not an important thing to check.
So blastocyst grading is a combination of numbers and letters. It’s a little bit of a strange way of thinking about it but if you think of a blastocyst as a football. What will gradually happen is that football will begin to inflate and if it’s less than what we call 20% inflated it gets a 1, if it becomes between 20 and 50% inflated ,it becomes a 2 and once it’s fully inflated it becomes a 3. Once that shell and left over from your egg which surrounds the embryo gets really paper thin and then it’s called a 4 and when it starts to the embryo starts to break through that shirt left behind that’s called a 5 or a hatching blastocyst and once it’s the embryo was fully out and that shells left behind that’s called a fully hatched or given a 6. So that’s the first part of the blastocyst grading, the second digit is to do with a letter which can be graded in different ways. Some clinics will do it A to C, some will do it A to E and that is measuring the inner cell mass which is the bit that goes on to make the baby. Ao an A grade would be nice big, chunky cells that are all stuck together, grade B would be those nice chunky graphic cells but they’re not quite as stuck together as they’d like, a C would be smaller in some clinics, a D will be if it’s starting to break down or an E grade would be if we can’t see one full stop and the second letter or third digit is based on this vector which is the bit that goes on to make the placenta and again that’s graded A to C in multi-clinics but can also be graded A to D. A means that nice cobbled street effects that you might see, B means it varies between how you look at it. If you think of it again as that football it might be good quality on one part of the football but not so good on the other part. At grade C means those nice small cobbled effects, the more like big paving slabs and those cells get bigger and bigger and bigger and a D would be degenerating.
Embryos can develop for up to five or six days before they are implanted into the mother’s uterus. Their development is evaluated according to consensus criteria established by experts. The criteria are based on morphology parameters: cell number, cell size, and symmetry at specific points of their development. More recently, time-lapse technology has also allowed embryologists to observe morphokinetic parameters that are associated with normal embryo development. Unlike prior methods, this tool allows us to observe embryo development as it happens, instead of just monitoring the embryo at predetermined points in time.
Overall, embryo classification systems use morphological parameters to determine the development potential of each embryo, as well as employing morphokinetic data as an added value to evaluate embryo viability.
In our clinic, we use the grading system established by the Spanish Society for Reproductive Biology. The scoring scheme classified embryos into four different categories, from the highest (A) to the lowest (D). It is worth noting that an embryo’s classification may change throughout its development – for instance, a grade A embryo on day three may not result in a grade A blastocyst on day 5.
Embryo quality could be evaluated by morphological parameters, as well as the timing of the cell division. Morphological parameters include the number of cells, stage specificity, fragmentation, and others. This grading system is normally used until the embryo reaches the third day of its development.
On day four, the cells within the embryo undergo compaction, which we can also use to determine the embryo’s overall quality. On day five, when the embryo reaches the blastocyst stage, we use a different grading system based on the blastocyst expansion rate and its hatching status. We measure the inner cell mass and the quality of the trophectoderm. The expansion of the blastocyst can be measured by examining the cavity of the embryo, which could be small, full, or expanded; or, if we see the blastocyst expand past – hatch out of – the zona pellucida, which indicates that it reached or is reaching the final stage of its development.
The same grading system is used for the trophectoderm, which later on becomes the placenta; we evaluate how many cells it consists of and how compacted the cells are. Evaluating embryos by the timing of the cell division requires a special time-lapse incubator. Using this approach, we can record the entirety of the embryo’s development, which gives us data that is provided into the software that can help to determine the embryos with the best potential for implantation.
The embryo quality grading system rates embryos by their morphology. The embryologists examine the embryos either on day three or day five of development to evaluate specific aspects of their growth. It’s important to understand that even a “perfect embryo” is not 100% guaranteed to be genetically perfect. Even in morphologically perfect embryos, there is a significant amount of chromosomally abnormal embryos. This mainly depends on the age of the woman and the quality of the sperm.
On the other hand, if the embryo is not perfect morphologically, it does not mean the embryo will not implant successfully; in fact, we have seen many pregnancies as a result of a morphologically imperfect embryo.
The aspects evaluated by the embryologists are different for embryos on day three than for those on day five of their development. There are also different grading systems used in the laboratories. The most common one grades a blastocyst with a number and two letters, for example, 4AB.
So when a patient undergoes an IVF treatment, whether through egg donation or using her own eggs, and sees a doctor’s note stating a day three embryo is grade 3, or that a blastocyst is rated 4AA, what does that actually mean?
Let’s look at day 3 embryos first. What happens on day 3 is that the embryo’s cells are dividing, but the overall size of the embryo is not increasing. A normal embryo on day 3 has between 6 and 10 cells, with the ideal number usually being 8cells. The quality of the embryo, however, does not only depend on the number of cells; other qualities need to be considered, such as fragmentation. Sometimes, as the embryo develops, the cytoplasm inside it breaks down into smaller fragments. An ideal embryo on day three does not have any fragments; a grade two embryo may have a few fragments, while a grade three may have a large amount. Cell size is another important factor – the cells should be synchronous, that is, they should have been divided in the same way and be of the same size. So, the ideal day 3 embryo should have eight cells, all the same size, with no fragmentation. However, it doesn’t mean that an embryo that deviates from these parameters will not reach the blastocyst stage or not implant correctly.
Day five embryos – embryos that reach the blastocyst stage – keep dividing while also increasing. It also starts developing a cavity inside; in an ideal situation, this cavity is surrounded by cells and has a mass inside. This mass is called the inner-cell mass, while the outside is called the trophectoderm. We grade the embryos with a number, which signifies how much the embryo has expanded. For instance, a grade 1 blastocyst has a cavity that takes up less than half of the overall size of the embryo. Grade 2 has a cavity that is larger than half. A grade 3 takes up almost the entire embryo, and a grade 4 is an expanded blastocyst with a very thin layer of cells surrounding it.
After we determine the size of the embryo, we observe the hatching process of the embryo, or rather, how far along in the process the embryo is. Hatching means exactly what you think it means. The embryo breaks the surrounding cell lining and starts expanding outwards. We assign letters, such as AA, AB, or AC to each embryo. The first letter grades the inner cell mass and the second grades the quality and the morphology of the blastocyst. This grading system allows embryologists to evaluate which embryos have more potential of resulting in a successful pregnancy.
Historically, however, grading systems such as this one have had a significant degree of subjectivity. That is, the grade given to each embryo depends on the embryologist. This is where technology comes into play. These days, many embryologic laboratories use a device known as an EmbryoScope, which allows us to monitor the cell division within the embryo and use sophisticated algorithms to reduce the subjectivity in the grading process.
However, keep in mind that a morphologically correct embryo does not necessarily mean it’s also genetically correct.
