Blastocyst Transfer (Day 5 Embryo Transfer)

The injection of a single sperm cell into an egg cell is called fertilization, and the single fertilized cell formed as a result is called the embryo.

In the first years of IVF treatments there was a very limited amount of information regarding embryo development. Due to the solutions used in embryo culturing not being as efficient as needed at the time, the transfer of the obtained embryos to the expected mother was done on the 2nd or 3rd day, which is called the cleavage period. Thanks to technology, knowledge and new developments in IVF treatment it's now possible to develop healthy embryos in a laboratory environment.

Embryos developed and monitored in the embryology lab reach the ``blastocyst`` stage at the end of day 5. Sometimes, slow developing embryos may not reach the blastocyst stage at the end of day 5. These embryos are monitored until day 6, and may turn into a blastocyst. In this case, embryo transfer is not done, but a frozen/thawed embryo transfer is planned.

16-18 hours after microinjection two nuclei inside the fertilized egg are observed. These contain the chromosomes that carry the genetic material from the mother and the father. Afterwards these nuclei fuse and disappear, and the embryo starts to divide. Within hours the embryo multiplies its cell count by continuously dividing. After microinjection, 2-6 cells are expected at the second day, and 6-12 cells are expected on the third day. After the third day embryo cells reach uncountably high numbers and the cells start to fuse. Towards the end of the fourth day, a fluid-filled cavity begins to form in the middle. Generally, on the fifth day, blastocyst is formed, which is surrounded by cells called 'trophectoderm' that will form the placenta, and consists of cells that will form the baby called the ''inner cell mass''.

The fluid-filled cavity inside the blastocyst starts to grow over time, and the blastocyst increases its volume. After reaching a certain diameter, the blastocyst leaves the protective membrane around it called ''Zona Pellucida'', and becomes ready to hold onto the uterus. This is called 'Hatching Blastocyst'.

There are three criteria determining the quality of a blastocyst; the width of the fluid-filled cavity, the number and shape of trophectoderm cells, and the cell number and shape of the inner cell mass.

Who is blastocyst transfer done to?

Research worldwide shows that a day 5 embryo transfer has a meaningful positive increase in pregnancy rates. However, it is not correct to do blastocyst transfer on every patient. Blastocyst transfer can be done only on patients with a high number of high quality embryos during cleavage period, to increase pregnancy rates.

In cases where the female patient is younger than 35 years old, there are no observed problems in the sperm quality of the male patient and when quality embryos are obtained, the chance for embryos reaching blastocyst stage on day 5 can be as high as 70%. However, occasionally, especially due to high age or serious sperm problems, embryos showing healthy development in early stages might not show the same quality growth in later stages. Sometimes these embryos may not reach the blastocyst stage at all, in this case the embryo transfer may be canceled. A good evaluation should be made when deciding on blastocyst transfer. Our doctor and embryologist will choose the best option for you and give you the necessary explanations.

Importance of clinic choice in blastocyst transfer

Blastocyst development depends on factors such as healthy embryo development, technical infrastructure of the clinic, experience of the embryologists and laboratory quality.

Therefore, when planning your treatment it is very important to choose the clinic that can plan your ideal treatment and apply it in the best way. 


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