Watch the webinar with Dr Danny Daphnis, Scientific Director at Mediterranean Fertility Center, Chania, Greece, in which he is explaining embryo grading.
Dr Daphnis started his talk by explaining the main aim of IVF, which is to have the live birth of a healthy baby. Everybody’s trying to get a good result. The main criteria for a successful IVF therapy are sperm quality, egg quality, embryo, and endometrial quality.
The hardest thing in all these aspects is that we have no way of actually testing the proper quality of either sperm, egg, embryo or endometrial receptivity. We only have indications. Dr Daphnis explained that:
‘When you’re talking to your gynaecologist or your IVF specialist or embryologist, remember that when they’re talking about good quality embryos or good quality eggs or very good endometrium, it’s always about indications. The only proof of a good embryo or a good endometrium is a pregnancy, a healthy pregnancy.’
Dr Daphnis, later on, explains that all embryologists and all doctors get trained on embryo transfers at the very final stage of their training. The reason is that it’s difficult. It’s the most important time of an IVF, it’s the most important time because if you get that wrong, all your efforts, and all your attempts have gone to waste. Therefore, doctors and embryologists need to realize how important it is to do a proper embryo transfer and select the best embryos for a woman to transfer back. The timing of embryo transfer, and embryo grading, are key ingredients for a successful IVF treatment.
Embryo transfer & timing
Most IVF centres nowadays perform a day-5 embryo transfer however, you can have a day-2 embryo transfer, day-3 embryo transfer or day-5 embryo transfer.
- Day-2 embryos – should have 2 to 3 cells
- Day – 3 embryo – should have around 6 to 8 cells
- Day – 5 embryo (blastocyst) – you can’t count the number of cells any more, usually, good blastocysts should consist of around 100-150 cells. Embryologists do not count cells, they look for a specific morphology
These three times are the best times to perform an embryo transfer. There’s no way to predict whether day 2, day 3 or day 5 is best for transfer. Dr Daphnis emphasized that not all embryos will reach day-5 or the blastocyst stage, not all embryos, are destined to become babies. Therefore, Dr Daphnis advises not to see blastocyst transfer as the best solution. Unfortunately, it is not always the best solution, it is the best solution if you have enough embryos on day 2 or day 3 of development and you’re going to have 1 or 2 good blastocysts on day 5.
If you have 2 or 3 embryos on day -2 or day 3, and it is allowed in your country to transfer them all back, it is not going to make any difference in your success rate if the embryo transfer takes place on day 3 or day 5. The only thing you will gain by waiting for the embryos to reach day 5 is to see if they continue to grow. However, people against blastocyst transfer will always tell you that a lady’s womb is a much better incubator than the incubators you can find in the labs.
Blastocyst transfer is not for everyone. Yes, it’s a very good solution, but it was initially made for embryologists o be able to select the best embryos for the patients.
According to Dr Daphnis, the first thing that embryologists want to see is an embryo with 1 cell with 2 pronuclei and 2 polar bodies. The 2 pronuclei are like 2 craters in the middle of the cytoplasm, and the polar bodies are 2 small balls that you can see just outside the cytoplasm.
Then on day 2,
you expect the embryo to be of 2 to 4 cells. On day 3, you expect the embryo to be 6 to 8 cells. On day 4 is what we call a morula stage, and from then on, the embryologists stop counting, the embryo becomes a mass, and on day 5 or day 6, depending on your lab, we expect the embryo to be a good-looking blastocyst.
Embryo grading (D2 & D3)
When it comes to embryo grading, Dr Daphnis stresses out that when we’re talking about the quality of the embryo, it all has to do with the morphology. Unfortunately, we do not have the technological means to know if the embryo is a baby.
- Grade 1 embryo – in the first picture, a grade 1 embryo is presented. There is no fragmentation (the fragmentation is usually visualized by very small droplets visible in picture 2). In the 1st picture, it’s a very nice embryo, it has equal round blastomeres and almost no fragmentation.
- Grade 2 embryo – it’s a good quality embryo with around 10% of fragmentation. They have mostly equal and regular blastomeres.
- Grade 3 embryo – is an embryo that starts to have quite a bit of fragmentation, the blastomeres are not equal in size any more. You will see small blastomeres and big blastomeres in the same embryo, and you might even have amorphous, so they are not quite round.
- Grade 4 embryo – it is a very poor quality embryo, these are completely fragmented embryos, the blastomeres range in various sizes, and these embryos, unfortunately, will never give us a pregnancy.
If you have a big cohort of embryos, you would expect to have a range of qualities. Usually, you would have some good quality, medium quality and some poor quality.
Embryo grading (D5 & D6)
Blastocyst grading is quite intricate, but it has made embryologist’s life quite easy. We can select with easiness the best embryos, the best quality embryos. The blastocysts are graded in 3 different ways, typically, you will hear the blastocysts are graded from 1 to 6, you’ll see a number at the beginning, then you’ll see it has two letters AA, BA, BB, CC, DD, etc.
First, Dr Daphnis explained what the inner cell mass and trophectoderm are.
- Inner cell mass – the part of the embryo which is starting to distinguish and will give rise to the actual embryo
- Trophectoderm – the outside cells that surround the inner cell mass, and those will start to give rise to the placenta later on.
When an embryologist grades the blastocyst from 0 to 6, it states its size.
- 0 – is a morula
- 1-2 – is an early blastocyst
- 3 – is a full blastocyst
- 4 – is an expanded blastocyst
- 5 – is a hatching blastocyst
- 6 – is a fully hatched blastocyst
The first letter means how big the blastocyst is. It doesn’t mean that if you have a 0, which is a morula, it is a bad blastocyst, it’s just not gone as far, at the time, that the embryo was checked. That is why Dr Daphnis emphasized that development is not a negative aspect. It’s not good to have, for example, a 5 or 6 – a hatching or a fully hatched blastocyst because you want that part of the development of a blastocyst to take place in your womb, not in the laboratory. The first letter signifies how good the quality of the inner cell mass is. A is the best, and C is the worst.
When the embryologists grade day-2, day-3 or day-5 embryos, their main aspect is to see if they have normal development if the number of cells and the morphology is good, the fragmentation is good. They select the best-looking embryo, unfortunately, there is no way to know if a good-looking embryo is a baby.
All embryo assessments are morphological. We look at the embryos, we look at the outside, we try to grade them, we know how the development goes, and this is what we try to assess. However, we always take into consideration that most embryo assessments are subjective, they’re done by different people, by different embryologists.
‘I’m quite a strict person, I will never grade a blastocyst as AA, or I will never give 8 cell embryo a grade 1 because I believe that if I do give this spectacular grading, it’s just like saying to the patient you’re going to get pregnant, and I know that IVF is never 100%. Therefore, I tend not to be so gracious with my gradings.’
Blastocyst transfer is not always the best solution because not all day-3 embryos will grow on to become blastocysts. More studies have shown that around 40% of day-3 embryos will reach the blastocyst stage. That means you have quite a bit of embryo wastage, as we call it, so if you have 10 day-3 embryos, only 4 of them will reach the blastocyst stage.
Dr Daphnis advises that these are general statistics, it doesn’t mean that it applies to you necessarily, but you should always keep that in mind.
If the embryo does reach the blastocyst stage, it still doesn’t mean it will give you a baby. Therefore, it’s a good way for an embryologist to be able to select the best one, but that doesn’t mean that by doing a blastocyst transfer, we shall get a pregnancy. However, if there is a good quality blastocyst, then the chances of pregnancy and implantation rate might increase.
are incubators in which the embryologists do not have to open and close them to look at the embryos, they already have a camera inside them, so we can look at embryonic development throughout the time that we have these embryos in the laboratory. That means we can consider looking at embryonic development from day 0 to day 5 and seeing how they develop. We try to find patterns that might help us select the best embryos, and we try to see how we can make what we call a non-invasive selection of the embryos just by looking at how they’re developing.
Artificial intelligence (AI) has been thrown into all these time-lapse incubators. These incubators are trying to predict the clinical pregnancy outcomes using a light microscope. They’re trying to find the patterns in how the embryos are dividing. If, for example, they divide too fast, then it might be good, whereas if they’re dividing too slow, it might be wrong, if they’re dividing all together, for example, instead of going from 1 cell to 2 cells to 3 cells and then to 4 cells, then that might have a detrimental effect. All these things are being looked at, at the moment.
Finally, Dr Daphnis added that technology is thrown into embryology, and hopefully, all this technology will help us make a non-invasive selection of the best embryos to transfer back to patients to achieve a healthy pregnancy.