The embryos are evaluated every day and on Day 5 of development, we determine a grade of the embryo depending on the expansion of the embryo and also the quality of the inner cell mass and the trophectoderm. So if we have embryo 5AA, we can say that it’s the best embryo because it’s fully expanded and it is starting to hatch (so it’s starting to go out of the pellucid zone) so it’s a very good sign because it helps to implant in the uterus. So when the embryo is 5 – it’s fully expanded with hatching and is the best and if we have AA evaluation that means that the inner cell mass is of high quality and also the trophectoderm has very high quality, so it makes the embryo to be a top quality embryo. Even though we cannot forget that as well, embryos with low quality can generate a pregnancy. Also embryos with very good quality can also degenerate. It’s true that it’s very important to have good embryos, but there are other things that can have a big influence on the result of the pregnancy.
When an embryo has reached the stage of 5AA and it is a good embryo. 5AA is a very good embryo, and it has good implantation potential.
A morphologically “perfect” blastocyst would be a AA; excellent inner cell mass and trophectoderm. When a blastocyst scores 5AA, the blastocyst is beginning to “hatch”. The number of the score indicates degradation of expansion of the embryo and the letters the score of the inner cell mass and trophectoderm. 5AA it would be a top grade embryo on day 5 or day 6. But it doesn’t mean that it’s an embryo in perfect condition, it would be morphologically top quality but we don’t know if it has any chromosomal abnormality.
A 5AA blastocyst is probably one of the best embryos that we can get, but, unfortunately, having a good morphology does not necessarily mean that the embryo is of good quality. It only means that the chances of having normal genetics and implantation are going to be higher.
When we grade an embryo 5AA, it means that it has almost done the hatching, and both the inner cell mass and trophectoderm are of top quality. The chances for one of these embryos, though it will depend on the age if we get this quality in egg donation, the pregnancy rate should be around 60-65% with just a single embryo transfer.
