Sperm, oocyte or embryo can be frozen and preserved in embryology laboratories. In the history of in vitro fertilization, egg (oocyte) cryopreservation which was the most difficult to do initially, is now widely available through developed medical technologies.
Initially sperm could be frozen, thawed and used very easily, then, embryo cryopreservation followed.
Oocyte cryopreservation can be useful in cases not only when a woman cannot get pregnant because of radio or chemotherapy against cancer but also when a woman hasn't found a suitable partner and has become over-aged. Because unlike in men, success rates fall below ten percent in women, even with IVF, after the age of 40 in women