What is an oocyte quality grading system?

The egg quality is difficult to evaluate when it’s “in viable”. That means when we don’t have it in the lab so the way it is evaluated is by your egg reservoir that you have. Usually a hormone test of your AMH which is Anti-Mullerian hormone and also a scan that will check the number of follicles you have in your ovaries. Scan tell us about the number of eggs you have available or the egg reservoir in your ovaries.
It is hard to predict what your egg quality is while they are in your ovaries but it is possible for embryologists like us to see the egg quality . Once eggs are collected and are given to embryologists in the lab uh for the purpose of IVF and ICSI. If you are doing IVF, again the eggs are sitting in a great cushion of cells called granulosa cells and it is not easy to visualize them immediately. It would be possible to see the quality of the egg that is fertilized or not fertilized the following day on day one. If we are doing a process called ICSI or micro injection, that process we remove the cells from around the egg and therefore can access the egg more accurately. We can see the zona around the egg which is the sort of shell the egg is held in, we can see the cytoplasm of the egg and have a better look at and be able to grade it better and say if it’s a good quality egg or a poor quality egg.
Generally as a common rule, we know that ladies that have a very low reservoir of eggs or their PCOS is very severe can produce poor quality eggs.

The oocyte grading system allows us to evaluate the eggs retrieved during a collection. They aren’t used as often as embryo grading systems, and the reason for that has to do with what happens to embryos on day three. On day three of embryo development, the effects of the male genetic material on the embryo are fully visible; thus, even the best eggs can still be greatly affected by the male factor.

Despite that, there is research that shows that the quality of the oocyte can indicate its chances for fertilization; oocytes displaying proper morphological qualities are more likely to undergo successful fertilization when compared to abnormal eggs. Additionally, implantation rates and pregnancy rates have been shown in studies to be affected by egg quality.

The first step in grading an oocyte’s quality is simple – we simply examine them under a microscope and judge its visual qualities – the colour, the size and shape, the morphology; all of these factors play an important role in evaluating egg quality. Then, we look inside the oocyte and examine its cytoplasm – whether there are any vacuoles or granules, which are indications of poor egg quality. We also look at the zona pellucida, which surrounds the oocyte and helps with fertilization; later on, it helps the embryo implant. Its thickness is an important factor in evaluating egg quality. Following that, we take a look at the polar bodies, which are the initial nuclei of the oocyte before fertilization.

We also evaluate the perivitelline space – the space between the oocyte and the zona pellucida. Finally, we judge the size of the oocyte – ideal eggs must be within very specific dimensions. The combination of all of these factors gives us a specific grading that evaluates whether an egg is okay to fertilize.

Egg quality grading systems have been developed more just over the recent years. Over the last sort of probably five or six years more than before that. Prior to that, we didn’t really look at eggs that much but more recently it’s been necessary to develop a system where we can grade eggs because we’re freezing eggs so we need to give them some kind of grading. It’s based on the smoothness of the cytoplasm, the smoothness of the membrane, the thickness of the zona pellucida which is the shell of the egg, the size of the egg, the presence or absence of the polar body. There are a couple of different factors taken into account when we look at grading an egg. We’re still not entirely sure how the grading of an egg links to its potential but we’re gathering as much information as we can and then obviously that’ll come out over time.

This is a very interesting question. In the embryology laboratory clinical embryologists indirectly evaluate oocyte quality and its competence by assessing oocyte maturation status as well as a pleiad of morphological features. To further elaborate on that, immediately following oocyte retrieval we assess the architecture and texture of the cumulus oocyte complex. At this stage oocytes are surrounded by several cells, namely cumulus cells, which support oocyte development. If the cumulus oocyte complex is compacted, probably the oocyte is immature. On the other hand, an expanded “fluffy looking” cumulus oocyte complex indicates that probably the oocyte is mature. Following this step, we have the choice to deeply assess oocyte quality by completely removing the cumulus cells, in order to have a direct and a clear picture of the oocyte. This procedure is well-known as denudation. At this point we are able to comprehensively assess both oocyte maturity and morphology. A mature oocyte is characterized by the absence of a visible nucleus and the presence of a small cell-like structure described as the first polar body. Only these oocytes are able to be normally fertilized, because only these have successfully completed the first meiotic division. Unfortunately, immature oocytes cannot be fertilized. It is generally recognized that, under normal circumstances, 85% of the retrieved oocytes have successfully matured and only the 15% of them are immature. Except for the maturation status, we can also evaluate several morphological features of the oocyte which are strongly associated with oocyte quality and its competence. Generally, clinical embryologists assess the size and the shape of the oocyte, the presence or the absence of intracytoplasmic features such as vacuoles, the architecture of the polar body as well as the characteristics of the zona pellucida. At this point it should be noted that the presence of some abnormal morphological features does not necessarily mean cycle failure. Morphological assessment of oocyte quality helps embryologists and clinicians to design the appropriate management strategy in order to increase the chances of in vitro fertilization success.

When oocytes are retrieved, we start by evaluating the status of their cumulus cells and their expansion. Fully mature oocytes are surrounded by several layers of expanded cumulus cells – the stage of their expansion and the number of cells give us information about the quality of the oocyte within. Unexpanded and compacted cumulus oophorus usually surround immature eggs, which are not ready to be fertilized; those oocytes are then discarded.

In the case of an ICSI treatment, the cumulus oophorus is removed, allowing us to examine the nuclear maturity and the morphology of the oocyte. Mature oocytes should be in metaphase II and display polar bodies within their perivitelline space.

Some eggs can show a nuclear structure called the germinal vesicle in their cytoplasm – in that case, polar bodies are not visible. Approximately 5% of all retrieved eggs have neither visible polar bodies nor germinal vesicles. These oocytes are called metaphase I oocytes. Oocytes in the germinal vesicle stage or metaphase I am immature and not ready for fertilization.

Upon egg retrieval, the IVF facility begins the work of evaluating their quality. At this stage, mature oocytes are separated from immature ones – the latter usually making up 20% of a single cycle’s retrieval. Once mature oocytes are isolated, morphological examinations begin – first, the eggs are judged by their size, as large oocytes are commonly associated with chromosomal abnormalities. Following that, eggs are screened for the presence of dark cytoplasm, vacuoles, or other aggregates within, as all of these are indicators of abnormal oocyte development.