The laboratory sends you a series of numbers and letters. This describes the embryos’ appearance at a specific point in time, not their future fate.
After the egg retrieval, each fertilised egg is monitored day by day. The report you receive uses two different systems depending on the stage at which the embryos were observed: the classification of early-stage embryos, up to day three, and that of blastocysts, on days five and six.
Day 0: retrieval and fertilisation, either conventional or via ICSI. Day 1: fertilisation is confirmed. A normally fertilised embryo shows two pronuclei; this is referred to as 2PN. An egg with 1PN or 3PN is abnormal and is not transferred.
Days 2 and 3: the cells are counted and their uniformity is assessed. A good-quality embryo has 4 cells on Day 2 and 7 to 8 cells on Day 3, of uniform size, with minimal fragmentation. A report such as ‘Day 3, 8 cells, grade A, 5 per cent fragmentation’ describes an embryo of good appearance.
Fragmentation refers to small cellular debris. Below 10 per cent, it is not significant; above 25 per cent, it indicates a poor prognosis.
By day 5 or day 6, the embryo develops into a blastocyst: a fluid-filled cavity, an inner cell mass that will form the foetus, and a trophectoderm that will form the placenta. The Gardner classification combines three pieces of information, for example 4AA:
A 4AA is excellent, a 3BB is good and transferable, a 4BC is average. The second letter, often overlooked, is in fact the best predictor of implantation in several studies.
It accurately predicts the likelihood of implantation: a good-grade blastocyst implants more often than a poor-grade one. This is why the best one is transferred first.
It does not predict chromosomal normality. A 4AA may be aneuploid, whilst a 3BC may be perfectly normal. There is a correlation, but it remains weak, and this is the rationale for pre-implantation genetic testing in older patients. Nor does it predict the child’s health: there is no data establishing a link between grade and subsequent development.
Finally, the grade is a human observation, made at a given moment by a particular embryologist. Two laboratories may grade the same embryo differently. Time-lapse videomicroscopy provides continuous observation, although its benefit in terms of live births has not been clearly demonstrated.
A useful rough guide for managing expectations: out of ten eggs retrieved, around eight are mature, six to seven are normally fertilised, and two to three reach the blastocyst stage. This attrition is normal; it does not indicate a laboratory problem. It also explains why the number of eggs retrieved is more important than the number of third-day embryos.
A blastocyst formed on Day 6 rather than Day 5 has slightly lower implantation rates, but still results in live births. It should not be ruled out. As for freezing, vitrification preserves high-grade blastocysts very well: implantation rates after thawing are comparable to those of fresh embryos, which means the ‘freeze all’ strategy comes at no real extra cost. The frozen embryo transfer process is detailed here.
The number of eggs retrieved and mature, the number of 2PN on Day 1, the number of blastocysts obtained along with their grade and the day they were frozen, and the fertilisation method used. These five pieces of information enable any doctor to understand your cycle, and they belong to you: a clinic must provide them to you in writing.
This is the Gardner grading system for a blastocyst: 4 indicates an expanded cavity; the first letter refers to the inner cell mass, and the second to the trophectoderm. A is the highest grade for each. A 4AA blastocyst is therefore an excellent one.
Yes. The grade predicts the likelihood of implantation, not chromosomal normality or the child’s health. Blastocysts graded B or C regularly result in live births.
As a rough guide: around eight mature eggs, six to seven fertilised normally, and two to three blastocysts. This attrition rate is normal.
Its implantation rates are slightly lower, but it does result in live births and should not be ruled out.
Source: https://fertilitegrece.com/en/blog/embryo-quality-blastocyst-grading/ — Triada Baloukoudis, IVF patient coordination in Greece. General information, not medical or legal advice. Printed on
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