Vitrification of Oocytes and Embryos

Currently, controlled ovarian hyperstimulation protocols commonly provide embryos in excess of those needed for fresh transfer. Therefore, techniques have been developed to store these surplus embryos in liquid nitrogen (referred to as cryopreservation) for an indefinite period of time without significant compromise of their quality. Based on data from the Centers for Disease Control and Prevention (CDC) from 2001 to 2004, about 18% of all IVF cycles in the USA used frozen embryos for transfer. In addition, data from the same registry compared live births per transfer using frozen and fresh embryos (25% versus 34% respectively) clearly showing that cryopreservation is an important adjunct to maximize the efficiency of every single patient’s oocyte retrieval. The fundamental objectives for successful cryostorage of cells in liquid nitrogen at -196°C can be summarized as follows: 1) arresting the metabolism reversibly, 2) maintaining structural and genetic integrity, 3) achieving acceptable survival rates after thawing, 4) maintain of developmental competence post thaw and, 5) the technique has to be reliable and repeatable.