Does embryo quality affect IVF success?

Embryo quality is probably one of the most important factors when we are talking about the chances of success. The reason is that there is a straightforward correlation between grade A embryos and implantation rates and the risk of miscarriage. This is not mathematics, it does not mean that if we transfer a grade A embryo, we are going to get pregnant. Unfortunately, other aspects cannot be assessed just in terms of morphology, for example, genetics, so in some cases, a great B embryo from a 27-year-old girl could have higher chances of success than a great A embryo of a 42-year-old woman. In this sense, we understand success in terms of a baby, not just getting pregnant.

Morphology is really relevant when we make decisions in a single cycle, but sometimes, it is not possible to compare different morphologies if the patients, for example, are of completely different ages. There is something else that we should assess to make sure that the embryo is of good quality.

The main scope of the embryo selection is to identify the embryo that has the highest implantation capacity to be transferred.
There are many ways to assess the embryos, for example, a grade A and grade B embryos are perfect and ideal for the transfer. That means that the embryos look as they should for the day.
For example grade A or grade B day 5 embryos have around 50 to 60 % chance to implant. On the other hand, if we don’t have grade A or grade B embryos to transfer and we only have available grade C embryos, then a grade C embryo will be transferred – that still has potential to implant.
Grade A and grade B embryos have the highest chance to implant and create a life birth where grade C embryos lower chances but still there is a chance for a life birth.
Sometimes patients do get disappointed and that they don’t achieve a lot of grade A or grade B embryos but we’ve seen life-births from grade C embryos as well.
Grading I would say it does affect the IVF success rate but it’s also subjective.

Embryo grading is a tool that embryologists use to determine which embryos have the highest implantation potential. Therefore, which ones are the best to transfer or to freeze. There are many ways of grading embryos. Here in our clinic, we use the grading that has been recommended by our Spanish Society for the Study of Reproductive Biology, and we classify the embryos into 4 different groups: A, B, C, D.

A is an embryo with the highest potential and D the poorest. Our decision on the embryo grade is based on the inner cell mass and the trophectoderm morphology. If we are talking about the blastocyst stage, we also consider the embryo development and morphokinetic parameters and other parameters such as fragmentation or blastocyst expansion.

Secondly, I would like to explain the difference between grade A and B blastocyst. On one hand, grade A blastocyst has an excellent structure and perfect timing, trophectoderm with many tiny blood cells, that’s a perfect embryo that appears in the book. On the other hand, a grade B embryo has a smaller inner cell mass or has a trophectoderm with a lower number of cells, but they are still great embryos and have higher implantation potential, so they can perfectly give you a pregnancy.

So, can embryos C or D implant? Yes, of course, they can. It is a matter of probabilities though. Even though the possibility of implanting isn’t as high as in embryos grade A or B, but no one can deny that they can still give you a pregnancy. Finally, I would like to highlight that even though embryo quality is important, it’s not the only factor, many other factors can also cause implantation failure. For instance, lifestyle, anatomical abnormalities and endometrial cavity, endometrial receptivity.

Recent studies have suggested that each patient has its own implantation window, that is the period when the uterus is receptive for the implantation. It could also be an aneuploidy rate, for example, if the patient is under or over 40. That is why it is crucial to treat each patient individually and perform all the tests needed to achieve the best outcome.