In some cases after performing in vitro fertilization, the number of embryos obtained is higher than the number that can be transferred. When this happens the excess embryos are frozen in order to increase the possibilities of that cycle in subsequent transfer attempts. In this way if a pregnancy is not achieved at the first attempt it is not necessary to start the whole treatment again, but simply to transfer one of these embryos.
In the case of a positive result, we can keep the embryos frozen to be used when the couple decides to have a child.
Also, there is the possibility of donating them.