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In the first years of in vitro fertilization, embryos developed in the laboratory were transferred to the mother at the 48th hour of fertilization. It was doubtful how long the simple salt solutions used as embryo culture media in those years would keep the fertilized egg alive. Morphological quality and growth rate (number of cells) of embryos, which are known to have a high effect on pregnancy rate as the media used, improved. As a result of this development, many in vitro fertilized embryos were transferred from 48 hours to 72 hours and higher rates of pregnancy began to be achieved.
Recently, embryo viability has been prolonged in the laboratory by using advanced medium systems and as a result, in the IVF centers, transfer rates have started to become widespread on the 5th or 6th day where higher pregnancy and implantation rates have been achieved. This is called blastocyst transfer. The final stage reached by the embryo before it attaches to the uterus is called the blastocyst stage. In our center, more than 500 blastocyst transfers were performed and 2-3. better results were obtained than day transfers.
Blastocyst transfer has several advantages:
• The chance to select embryos with better developmental potential and uterine adaptation and consequently have better outcomes in recurrent pregnancy failures
• Reduces the possibility of multiple pregnancies by transferring fewer embryos with high viability
• To be able to observe embryo development better
• Freezing embryos during the period when they have the highest growth potential, ie blastocyst stage
• To be able to perform trophectoderm biopsy in preimplantation genetics centers and to eliminate ethical problems since this tissue is non-embryonic.
• To give an opportunity to the methods in which embryo viability can be examined.
Nowadays, different characteristics of blastocyst are taken into consideration in order to increase success. The most important of these is the quality and developmental potential of blastocysts as in day 2 and day 3 embryos. Transferring the blastocyst of the best quality and the most advanced stage of development to the patient will significantly increase the pregnancy rate. In addition, better results can be obtained by transferring the blastocyst outer shell after peeling with special methods with the method which is also used in our center. In order for the blastocyst to hold onto the uterus, it must be stripped of its outer shell. There is a possibility that this sheath could not be broken in people who had previously undergone blastocyst transfer but had no pregnancy.
Methods for increasing the success of blastocyst transfer are still one of the most intensively researched subjects all over the world. In general, it is accepted that the transfer in blastocyst stage does not increase the chance of pregnancy but increases the retention rate per embryo, thus enabling the transfer of fewer embryos and reducing the risk of multiple pregnancies.