Table 1.

Indications for cryopreservation in ART practice.

	Elective	Non-elective
Oocytes	Oocyte donation, oocyte banking Avoids the need to match donor's and recipient's cycles, and addresses demand for donor oocytes, thereby alleviating waiting lists (32)	Medical oocyte freezing In women about to undergo gonadotoxic treatment for cancer or other conditions, or with a medical pathology that impairs fertility, such as severe endometriosis (41) or genetic conditions including Turner's syndrome (42)
	Social freezing Allows women wishing to defer childbearing to preserve their fertility in anticipation of age-related fertility decline (33, 34) Oocyte cryopreservation can provide a feasible alternative where embryo cryopreservation is not an option because of religious, moral or ethical objections, or restrictive legislation (40)	Incidental oocyte freezing Emergency freezing in IVF when sperm is not available on the day of oocyte retrieval (43) Storage of “spare” oocytes during IVF (44)
	Clinical oocyte freezing Accumulation of oocytes to increase likelihood of future success in cases of poor responders or recurrent implantation failure (35, 36), or to increase their availability for PGT (16)
	Transgenders In the case of female to male change, provides the opportunity to preserve oocytes for future fertilization by a partner or sperm donor (37, 38)
Embryos	Preimplantation genetic testing (PGT) PGT is facilitated by the opportunity to use the freeze-all strategy for storing embryos for transfer in subsequent cycles after testing (27) Patient's or physician's preference The ability to store surplus embryos can reduce the number of embryos transferred during a fresh cycle and thus minimize the risk of multiple pregnancy, reduce the need for repeated stimulation cycles, and increase cumulative pregnancy rates (44)	Elevated progesterone Elevated progesterone in the late follicular phase has a negative impact on pregnancy rate, although the reasons for this are not entirely clear (45–47) Avoidance of OHSS Embryos may be cryopreserved rather than proceeding with a fresh embryo transfer to allow ovarian recovery and thus prevent OHSS when excess follicle development has occurred following ovarian stimulation in the IVF cycle (25, 48)