What is a Blastocyst Transfer?
Blastocyst transfer is a method used to improve embryo selection efficiency and achieve higher pregnancy rates. Normally, in IVF treatment, embryos are transferred to the uterus when they are usually 2-3 days old. In blastocyst transfer, embryos are transferred when they are 5-6 days old.
A blastocyst is a stage in the development of an embryo where the embryo cells have undergone several divisions and have divided into more cells. At this stage, the embryo has two main parts: the outer cell layer called the trophectoderm and the inner cell mass.
Studies have shown that pregnancy rates are higher in 5th-day embryo transfers. Particularly in couples with a large number of good quality embryos on the 3rd day, allowing the embryos to grow until the blastocyst stage and transferring the best quality embryos increases the chances of pregnancy success.
In blastocyst transfer, fewer embryos are used as they are in a more advanced stage of development, resulting in higher pregnancy rates. However, since this procedure requires more expertise, it should be performed by specialized medical personnel.
What Does Embryo Quality Depend On, Can It Be Improved?
The quality of the embryo is determined by the genetic makeup of the couple (the quality of sperm and eggs). In addition, the accurate determination of the dosage of medication used for egg stimulation and the proper timing of the trigger injection are also effective.
Another important factor is the conditions of the embryology laboratory. The equipment and quality of devices used, as well as factors such as temperature, humidity, and gas levels in the laboratory, can also affect embryo quality. At British Cyprus IVF Hospital, we have a state-of-the-art embryology laboratory equipped with the latest technology and experienced embryologists.
What is the Blastocyst Stage?
During the process of in vitro fertilization (IVF), there are different options for embryo transfer. Some of these options include transferring embryos on the 2nd day, 3rd day, or 5th day. In cases where the number of embryos is low (1-2 embryos), transferring the embryos on the second day is preferred, as it is believed that these embryos can develop better in their natural environment.
In cases where the number of embryos is high, transferring the embryos on the 3rd day or 5th day is preferred in order to observe the further development of the embryos and select the best quality one. During this process, there are certain criteria used to determine which embryo is superior.
Indicators such as the number of cells within the embryo (division rate), the equality of cells, the condition of the intracellular cytoplasm, and the appearance of the embryo’s shell provide information about the embryo quality.
The evaluation criteria used for embryos on the 3rd day and earlier are inadequate for the 4th day and beyond. This is because the embryo undergoes a different stage of development on the 4th day and beyond, and it begins to change in shape and volume. At this stage, the embryo is referred to as a blastocyst and is evaluated differently due to its unique structure. Since there are numerous cells in the blastocyst stage, it is impossible to count them. Therefore, the quality of the embryo is determined by analyzing features such as the arrangement and appearance of cells, the condition of the cavity known as the blastocoel, and the presence and physical state of the inner cell mass (ICM) region.
How Many Cells Does the Blastocyst Have?
Blastocyst is an embryo consisting of 60-100 cells. This embryo has the highest probability of implantation in the uterus.
Embryo Developments and Quality Assessment
Morula (CM): It is the stage before reaching the blastocyst stage. The embryo has not yet formed the cavity (space), but the cells have started to come together to prepare the structure before cavity formation. It is impossible to count the cells at this stage.
Early Blastocyst (1): The embryo at this stage is classified as early blastocyst. Cavity formation has begun, but the inner and outer cell differentiation has not yet occurred. At this point, the embryo can already be referred to as a blastocyst. It is of better quality than the morula stage and has a higher chance of pregnancy.
Early Blastocyst (2): The intra-cellular cavity has expanded, but the inner and outer cells are still not fully separated. This indicates that the embryo has passed its viability and many controls during blastocyst formation. The embryo will now continue to expand and the cells will start to differentiate internally.
Blastocyst (3): When the embryo reaches the 3rd blastocyst stage, the condition of the cells is observed more closely. Features such as the inner cell complex, the arrangement and quantity of the outer cells, and the thickness of the embryo’s shell can be classified. In this stage and beyond, embryos are named not only by stage number but also by adding letters indicating the quality of the inner and outer cells. After the stage number, a letter for the inner cell quality is added first, followed by a letter for the outer cell quality.
Blastocyst (4): The blastocyst in the 4th stage begins to fully demonstrate its potential. The embryo has expanded, and the embryo’s shell has become thinner. The inner cell is clearly visible, and the arrangement and relationships of the outer cells are evident.
Blastocyst (5): After a certain stage, when the shell has thinned significantly, the embryo starts to protrude for implantation in the uterus. The embryo that has started to protrude is now considered a blastocyst in the 5th stage. The evaluations at this stage are the same as the previous stage. Embryos that reach this level are also suitable for genetic diagnosis biopsy.
Blastocyst (6): Blastocysts can only survive in the laboratory environment until this stage. As seen in the image, the embryo has completely emerged from its shell and now needs to attach to the mother’s uterus. If implantation does not occur after this stage, the embryo cannot survive.
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