Table 2.

Comparison of oocyte and embryo cryopreservation methods.

Freezing procedures
Conventional slow-freezing method	Vitrification
(1) Standard 0.25 ml straws	(1) Several devices for loading embryos and oocytes (conventional straws, open pulled straw, cryoloop, cryoleaf, cryotop, etc.)
(2) Low cryoprotectant concentration	(2) High cryoprotectant concentration/ reduced volume and time with vitrification solution
(3) Seeding at −5 to −7°C, controlled slow cooling (0.1 to 0.3°C/min)	(3) Ultra-rapid cooling rates (−2500°C/min or 20000°C/min using OPS and cryoloop)
(4) Plunging at −30 to −70°C and storage in liquid nitrogen (−196°C)	(4) Plunging into liquid nitrogen (−196°C)

Adapted from Pereira and Marques, 2008 [3].