The embryo transfer usually takes place on the third day after the egg collection, in the embryonic stage of 6-8 cells. However, quite often the embryo transfer that is decided to take place at the blastocyst stage (5th -6th day of embryonic development) and it has been shown that the selection of embryos with good quality at this stage has better potential and gives higher pregnancy success rates.
Blastocyst stage embryo transfers are indicated to be performed in the following cases:
- When there is history of implantation failure from embryo transfers with second or third day stage embryos
- When we have an excess of embryos on the first or third day of development, with similar quality and equal morphological “scoring”. In these cases, the delay of embryo transfer towards the blastocyst stage is chosen, in order for the embryologists to manage to select the most capable embryos to be transferred.
- When preimplantation diagnosis (PGD/PGS) is needed. In these cases the embryonic biopsy takes place on the 3rd or 5th day of development and the embryo transfer has to take place a day or two later (in fresh cycles), meaning necessarily on the 5th or 6th day respectively, because in the meantime the genetic analysis has to be done by the geneticists and it takes up to24 hours, until the answer for the genetic material of the embryos is announced, so that the suitable embryos for embryo transfer can be selected.
Advantages
- Shifting of the “Implantation window”
The Implantation window is a very short period within every woman’s cycle, during which the endometrium completely changes its gene’s expression profile and expresses hundreds of different proteins that are enabling just for a few hours the reception of the foetus for implantation. This short period that lasts no more than 24 hours is called the “implantation window” and is not the same in all cycles or for every woman. Unfortunately, we are not able to identify the exact implantation window but we assume that in most women it is “open” on the 3rd day of embryonic growth. For this reason, embryo transfers are usually attempted on the 3rd day of embryonic development. But our experience shows us that not all women have their implantation window open on the 3rd day but on the 4th or 5th or even the 6th day. These are the women who benefit the most from a blastocyst stage embryo transfer.
- Another basic advantage of embryo transfer at the blastocyst stage is the ability to select the most capable embryos for embryo transfer based on their morphological characteristics that are more visible for evaluation at this stage by embryologists.
- The method of embryo transfer at the blastocyst stage, according to some studies, will more likely give better results in terms of implantation and abortion.
Disadvantages
- Cancellation risk
- Less available embryos
The only disadvantage of applying embryo transfer at the blastocyst stage is that eventually the embryos may not be able to survive up to this stage of development and unfortunately sometimes the attempt of an embryo transfer might be cancelled or the embryo transfer has to take place with fewer embryos. This risk, which is in fact plasmatic, is used as an argument by colleagues who either lack the knowledge or are hesitating to apply embryo transfers on the 5th day. But the truth is that embryos that have never managed to reach the blastocyst stage could have never lead to a pregnancy either.
