When making test tubes, which one should you choose 4BB or 3AC blastocysts, and which one is better?
Source: LelaiwaPublished: 2025-11-07
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"Doctor, one of these two blastocysts is 4BB and the other is 3AC." In the consultation room of the reproduction center, such questions occur every day. For IVF families, the choice of blastocyst is directly related to the success or failure of transplantation. Faced with professional grade codes, many patients are confused. Let's have a chat today!
During the blastocyst transfer stage of IVF treatment, doctors usually give a grade score based on the development of the blastocyst. This scoring system is an important basis for assessing the quality and development potential of the blastocyst. Professor Li, chief physician of the department of reproduction, said: "In clinical practice, 4BB blastocysts are usually considered to have more advantages than 3AC blastocysts, but this is not an absolute conclusion and requires a comprehensive analysis based on the specific meaning of blastocyst grade."
1. What do the "numbers + letters" of the blastocyst level represent?
The expression method of blastocyst level may seem complicated, but in fact it has clear specifications. It usually consists of "1 number +2 letters", such as the common 4BB, 3AC, etc., each character corresponds to key information about blastocyst development.
tThenumber (range 1-6)represents the development stage of the blastocyst. The higher the number, the more mature the blastocyst develops and the closer it is to the implantation state. Level 1 is the early blastocyst, with the blastocyst cavity less than half the volume of the embryo; Level 3 is the fully expanded blastocyst, with the blastocyst cavity completely occupying the volume of the embryo; Level 4 is the expanded blastocyst, with the volume of the blastocyst cavity increasing and the zona thinning, which is one of the stages that is more conducive to implantation; and Level 6 represents the blastocyst that has been incubated and the blastocyst has escaped from the zona pellucida.
Thefirst letter (A-C)after the number is related to the "source" of the fetus-the quality of the inner cell mass. The inner cell mass will develop into the fetus in the future, and its quality directly affects the healthy development of the fetus. Grade A means that the number of cells in the inner cell mass is large and closely arranged, which is an excellent grade; Grade B means that the number of cells is small and the arrangement is loose; Grade C means that the number of cells is small and the quality is the worst.
The second letter (A-C)corresponds to the quality of the trophoblast cells, the "predecessor" of the placenta. Trophoblast cells will develop into the placenta in the future and be responsible for delivering nutrients to the fetus. The grading standard is consistent with that of the inner cell mass. Grade A is excellent, with cells arranged tightly and in regular structure; Grade C is the worst, with cells arranged loosely and in irregular structure.
Professor Li emphasized: "On the premise that the development stage of blastocyst is the same, there is a clear reference for the ranking of the quality of the embryo: AA, BA, AB, BB, CA, AC, CB, BC, CC. This ranking can help patients initially judge the quality of the blastocyst, but it must be combined with a comprehensive evaluation of the development stage."
2. What are the core differences between 4BB and 3AC blastocysts?
After understanding the grading rules, we specifically disassembled the characteristics of the two common blastocysts, 4BB and 3AC, and made intuitive comparisons from both aspects of development stage and cell quality.
4BB blastocyst: The development stage is more advantageous. The number "4" indicates that the blastocyst is in the expansion stage. At this time, the blastocyst cavity has been significantly expanded, the zona pellucida has become very thin, and the overall activity and implantation ability of the blastocyst are in a good state. The two "Bs" respectively represent that both the inner cell mass and the trophoblast cells are of Class B-although the number of cells in the inner cell mass is not large and the arrangement is slightly loose, they have normal differentiation potential; the trophoblast cells are also medium in number and have insufficient structure. Compact, but can meet the basic needs of subsequent placental development.
3AC blastocyst: The inner cell mass is of high quality but the trophoblast has shortcomings. The number "3" indicates that it is in the fully expanded stage, and the blastocyst cavity just fills the entire embryo, but compared to the level 4 blastocyst, the development maturity is slightly lower. The first letter "A" is the outstanding advantage of this blastocyst, which means that the inner cell mass has a large number and close arrangement, and has a strong potential to develop into a healthy fetus in the future; but the second letter "C" exposes obvious shortcomings-The number of trophoblastic cells is small and the structure is loose, which may affect the formation and function of subsequent placenta, thereby increasing the risk of insufficient nutrient supply after implantation.
Overall, although 4BB blastocysts do not have the outstanding advantage of A-level cell quality, they are more mature in the development stage and more balanced and stable overall development potential. However, due to the poor quality of trophoblastic cells in 3AC blastocysts, even if the inner cell mass is of high quality, problems may occur in the nutrient transport process after implantation, which to a certain extent offsets the advantages of the inner cell mass. Professor Li explained: "Blastocyst implantation is a 'teamwork' process. The development stage determines the 'implantation competitiveness' of the blastocyst. The inner cell mass and trophoblastic cells are responsible for 'fetal development' and 'nutrient supply', respectively. Shortcomings in any link may affect the final result. Relatively speaking, 4BB blastocysts with more mature development stages have a higher fault tolerance rate."
3. The blastocyst level is not an "exclusive answer"
It needs to be specially reminded that the blastocyst level is only an important reference in the treatment of IVF. One of the indicators is not the "exclusive answer" that determines the success or failure of transplantation. Professor Li emphasized: "In clinical practice, we will comprehensively evaluate various factors, such as whether the maternal uterine environment is suitable-whether the endometrial thickness is in the appropriate range of 8-12mm, whether there are endometrial polyps or adhesions, etc.; The maternal endocrine status, such as whether the progesterone level is up to standard, as well as the patient's age, underlying diseases, etc., will all have an impact on the success rate of transplantation."
Therefore, when faced with confusion about blastocyst selection, patients should not judge for themselves based on grade alone. The correct approach is to fully communicate with the attending reproductive doctor. The doctor will formulate a personalized transplant plan based on the patient's specific physical condition, detailed evaluation report of blastocyst, and previous clinical case experience. "Each patient's condition is unique. A blastocyst that is suitable for others may not be suitable for you. Professional medical evaluation is the most reliable basis." Professor Li finally said.
For more on fertility preparation, second/third-generation IVF, and overseas, U.S., Thailand, Malaysia, America or Cambodia IVF, scan the QR code on the right or call lelaiwa's hotline+852 6145 8043!
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