Embryos not used in the current cycle may be cryopreserved. Cryopreservation is often accomplished with vitrification, a fast freezing procedure. Vitrification is assumed to avoid cryoinjury by decreasing the development of intracellular crystals.[35] All embryos may also be frozen in patients at risk for ovarian hyperstimulation syndrome (discussed additional in https://www.ivf.com.mx/