Sometimes delayed transfer, i.e. of vitrified embryos, is not recommended. It is essential that the vitrification process is followed perfectly to ensure the safety and integrity of the blastocysts.
In addition, it must be taken into account that not all embryos are capable of reaching the blastocyst stage. If it is decided to vitrify all embryos at day 5 of development, the transfer may have to be cancelled because there are no embryos left. Therefore, it is necessary to analyze the risks of each embryo individually.