Blastocyst Embryo Transfer

One of the topics of interest in in vitro fertilization (IVF) treatment is blastocyst embryo transfer. In natural pregnancies, the egg released from the ovary is captured by the fallopian tube and moves toward the uterus. The fertilization of the egg by sperm results in a single-celled embryo. The embryo progresses through sequential cell divisions while moving toward the uterus within the fallopian tube.

An embryo that reaches the uterus on days 5 to 7 of its development and consists of approximately 100 cells is called a blastocyst. During the blastocyst stage, the embryo expands in volume, exits the surrounding zona pellucida (the protective layer), and implants into the uterus under suitable conditions through a process called implantation.

In IVF treatments, embryos are obtained by fertilizing sperm and eggs in a laboratory environment, and after reaching certain developmental stages, they are transferred to the uterus. Blastocyst embryo transfer occurs after waiting for the embryos to reach the 5th or 6th day stage in the laboratory.

In the early years of IVF applications, due to limited information and experience regarding embryo development, as well as unfavorable laboratory conditions and technical capabilities, embryo transfers were typically performed during the early cleavage stage (days 2 and 3 of embryo development). Over time, with the increase in knowledge and technical capabilities, it became possible for embryos to develop to the implantation stage in a laboratory environment. Today, the rates of blastocyst transfer vary depending on patient characteristics, treatment history, and the infrastructure of the IVF clinic.

Studies conducted both in our clinic and worldwide indicate that pregnancy rates are significantly higher when embryo transfers are performed on day 5 instead of day 3. However, blastocyst transfer may not be suitable for every couple. Especially for couples with a good number of high-quality embryos on day 3, allowing embryos to grow to the blastocyst stage enables the selection of embryos with a higher potential for pregnancy.

To reduce the risk of embryos being damaged by the external environment, multiple embryos are generally transferred during cleavage embryo transfers to increase the chances of pregnancy. However, transferring multiple embryos carries the risk of multiple pregnancies (twins, triplets). In recent years, limits have been set on the number of embryos that can be transferred to prevent multiple pregnancies.

Especially for couples with more than a certain number of embryos, performing a blastocyst transfer (days 5-6) instead of an early embryo transfer (days 2-3) allows for the selection of embryos with a higher potential for pregnancy, increases the chances of pregnancy after a single embryo transfer, and reduces the likelihood of multiple pregnancies. However, in some patients with a limited number of embryos, early embryo transfer may still be preferred.

Blastocyst transfer is generally preferred for women under the age of 35, particularly for couples with 5 or more good-quality embryos on day 3, to make embryo selection more efficient and achieve higher pregnancy rates. Additionally, it is frequently preferred in couples where previous attempts to achieve pregnancy with good-quality embryos on days 2 or 3 have failed, in couples who do not wish to have multiple pregnancies (as selected single blastocyst transfer), and in couples where a large number of embryos have been obtained but do not want the remaining embryos to be frozen.

The rate of good-quality day 3 embryos reaching the blastocyst stage is approximately 30-50%. However, due to reasons such as poor egg quality or advanced maternal age, some couples may have lower rates of blastocyst formation or may not obtain blastocysts despite repeated treatments.

If the embryos do not reach the blastocyst stage, the transfer is canceled. Therefore, couples planned for blastocyst transfer should be informed about these possibilities that may arise during treatment. The likelihood of reaching the blastocyst stage depends not only on the quality of the eggs and sperm but also on the technical infrastructure and appropriate laboratory conditions available in the clinic.

In some laboratories, due to technical inadequacies, transferring or freezing embryos at the blastocyst stage on day 5 may not yield as good results as transferring them during the cleavage stage. Your treating physician will provide you with information about the most suitable and potentially successful embryo transfer day based on all this information and the probabilities involved.