In addition to this, it is also commonly used for couples who have previous treatments where they have not able to become pregnant although they had quality embryos on the 2nd and 3rd day, for couples who do not want multiple pregnancies (twins), and couples who have many embryos but do not want their embryos to be frozen.
There are different embryo transfer options available for IVF treatments. These options include transferring the 2, 3, and 5-day old embryos. Couples who have a low number of embryos (1-2 embryos) may think that these embryos can develop better in their natural environment and as a result, choose to transfer them on the second day. However, in cases where there are many embryos, the couple may want to wait a little longer to choose the best and most quality embryos and therefore prefer to conduct the embryo transfer on the 3rd or 5th day. There are certain criteria to determine which embryos are better during this period. The number of cells within the embryo (speed of multiplying), the equality between cells, the condition of the cytoplasm within the cells and the appearance of the embryo shell provide information on the quality of the embryo.
The embryo evaluation criteria used on the 3rd day and before are insufficient to evaluate the embryo after the 4th day. This is because the embryo changes its shape and volume on the 4th day. At this stage, the embryo is called a blastocyst and is evaluated in a different way according to its own structure. Due to there being many cells at the blastocyst phase, it is impossible to count them all. This is why the location and appearance of the cells, the situation of the gap called the cavity, the inner cell mass and its physical condition are analysed and the quality of the embryo can be determined.
Evaluation of Embryo Development and Quality on the 4th Day Onward
Morula (CM): This is the phase before the blastocyst phase. In this phase, the cavity within the embryo has not yet formed, however the cells have gathered together in preparation to produce the cavity structure. During this phase, it is impossible to count the number of cells. Morula (CM): This is the phase before the blastocyst phase. In this phase, the cavity within the embryo has not yet formed, however the cells have gathered together in preparation to produce the cavity structure. During this phase, it is impossible to count the number of cells.
Early Blastocyst (1): At this phase, also called the early blastocyst phase, the embryo is classified as phase 1. This is when the cavity has started to form, although internal or external cells cannot be distinguished. The embryo in this phase can now be called a blastocyst. In terms of quality, it is better than a morula and it provides a higher chance of pregnancy.
Early Blastocyst (2): The cavity is wider, but the internal and external cells cannot be distinguished yet. This shows how alive the embryo is and that it has passed many check-ups before the blastocyst phase. Now, the embryo starts to expand and the cells start to divide.
Blastocyst (3): When the embryo has reached its 3rd blastocyst phase, the cells can now be seen better. The internal cell complex, the location and number of external cells, the thickness of the embryo shell and other such specifications can be classified. After this phase, the embryos are not only classified with their phase number, but with letters that state the condition of their internal and external cells. After the phase number, letters for first the internal cell then the external cell quality are added.
Blastocyst (4): The blastocyst in the 4th phase starts to fully reveal its potential. The egg has expanded and the shell of the embryo has become thinner. The internal cell is easily visible, and the location and relationships between the external cells are clear.
Blastocyst (5): After a certain period, once the embryo shell has become suitably thin, it then starts to expand in order to attach to the wall of the womb. The embryo that is starting to come out of its shell is now evaluated as a blastocyst in the 5th phase. The other evaluations are the same as the previous phase. Embryos that reach this phase are also suitable for a biopsy for genetic screening.
Blastocyst (6): In the laboratory environment, it is only possible for a blastocyst to survive up to this phase. As can be observed in the image, the whole of the embryo has now come out of its shell and has attached to the mother’s womb. After this phase, if the embryo does not attach to the womb, it will not survive.
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