First published [15-10-2026]
A blastocyst grade such as 4AA has three parts. The number (1 to 6) shows how far the blastocyst has expanded or started to hatch. The first letter describes the inner cell mass, which can form the baby. The second letter describes the trophectoderm, the outer layer that mostly forms the placenta. A and B describe a stronger or more moderate look, and C a weaker one. These are descriptions of appearance on the day, not promises.
Key takeaways
Embryo grading is how an embryologist describes, in a few symbols, what an embryo looks like under the microscope. It can be done on cleavage-stage embryos, but it is most often used for blastocysts, which are usually graded on day 5, day 6, or occasionally day 7 after fertilisation.
The notation helps the lab compare embryos and plan which to freeze or transfer. It is a visual note, not a genetic test, so it should not be read as a guarantee. To see how embryos reach this point, read our day-by-day guide to embryo development.
The number follows how much the fluid-filled cavity has grown and whether the blastocyst has begun to push out of its outer shell, the zona pellucida. Labs word this a little differently, so confirm your clinic's key.
Each letter grades a separate group of cells, so they are read in order, ICM first and trophectoderm second.
A 4AA is an expanded blastocyst with an A-grade inner cell mass and an A-grade trophectoderm. On appearance, both cell groups look strong on that day.
It still does not promise implantation or normal chromosomes. Its meaning depends on your age, any genetic test results, how many embryos you have, your womb preparation and your clinic's transfer policy.
A 5AA is a hatching blastocyst with A-grade cells in both groups. The 5 says it is further along than a 4, while the letters describe the cells.
It is usually regarded as a strong appearance, though it is not automatically superior to every 4AA. The time of assessment, the freezing policy and your own situation all count.
A 3BB is a full blastocyst whose inner cell mass and trophectoderm are both graded B. It has reached the blastocyst stage, but the cells look less robust than an A grade.
That is no reason to write it off. Pregnancies and live births do come from B-grade embryos. Whether it is transferred or frozen depends on your whole clinical picture and your clinic's laboratory policy.
Holding an embryo report you can't decode? Bring it to a consultation and our team will walk you through every symbol and your options.
The letters are not averaged into one score because the two cell groups do different jobs. Ask how your clinic ranks embryos with different combinations.
In general, embryos with stronger-looking features tend to have better implantation potential across groups of patients. However, an embryo grade cannot predict the outcome for an individual transfer. It describes the embryo's appearance at the time of assessment, and grading can vary depending on when the embryo is checked, the embryologist's assessment and the laboratory's grading criteria.
A higher grade can be encouraging, but it should always be considered alongside other clinical information rather than treated as a guarantee.
No. Embryo grading describes the embryo's appearance and development under a microscope. It cannot confirm whether the embryo has the expected number of chromosomes or rule out genetic conditions.
If your fertility specialist discusses preimplantation genetic testing (PGT), ask what the test is designed to detect, its limitations, whether embryo biopsy is needed, how the embryos will be stored and how the results could influence your treatment plan. Testing has limitations and cannot guarantee pregnancy or a healthy baby, or eliminate every risk during pregnancy.
Embryo grading is one part of the selection process. Your fertility team may also consider:
The embryo with the highest grade is not guaranteed to result in pregnancy. Your fertility specialist should explain why a particular embryo is recommended, how its grade is interpreted, and what the limitations are. Embryo selection is based on the overall clinical picture, not the grade alone.
To understand how embryos are assessed and prioritised during IVF, read more about embryo selection in IVF.
In an embryo grade such as 4AA, the number indicates the blastocyst's stage of expansion, while the two letters describe the inner cell mass and trophectoderm. A 5AA is a hatching blastocyst with A-grade cell groups, while a 3BB is a full blastocyst with B-grade cell groups. These grades help embryologists assess and prioritise embryos, but they cannot confirm chromosomal health or guarantee pregnancy.
Related reading: What is a blastocyst? | Blastocyst transfer success rates | Frozen embryo transfer | Embryo implantation after IVF
Want to understand what your embryo grades mean for your IVF treatment? Book a consultation at Dr. Aravind's IVF Fertility & Pregnancy Centre and ask your fertility team to explain your report and available options.
Book an IVF consultation →Medical disclaimer: An embryo grade describes its appearance at the time of assessment. It does not confirm chromosomal health or guarantee implantation, pregnancy or live birth. Your embryologist and fertility specialist should interpret your report in the context of your individual treatment plan.
In clinics that use this notation, 4AA reads as a strong-looking embryo, but it is not a promise. A 5AA or 4AB embryo may be just as suitable.
It is a full blastocyst where both cell groups look moderate. Depending on your clinic's rules and your own case, it can still be frozen or transferred.
Not always. The first digit shows how far the blastocyst has expanded or started hatching, and the letters describe the cells. Both grades can look excellent.
It can. How an embryo looks is not the same as how healthy its chromosomes are, and no grade can predict the outcome of one pregnancy.
No. A grade carries no information about sex. That kind of information only comes from genetic testing, which is bound by medical, ethical, and legal rules.
