Occasionally after IVF or ICSI, people have a number of unused embryos after their first cycle. Some people choose to freeze them for use in later treatment cycles or to donate for use in others’ treatment, research purposes or training. Your chances of becoming pregnant with a thawed frozen embryo are not affected by the length of time the embryo has been stored. But not all embryos will survive freezing and eventual thawing when they come to be used. Very occasionally no embryos will survive.