Vitrification and the demise of fresh treatment cycles in ART.

The advent of vitrification has transformed the therapeutic landscape in assisted reproductive technology. Clear evidence for this is provided by the dramatic rise in the number of frozen embryo transfer (FET) cycles being carried out annually. In this review, we examine the reasons that underlie this trend and the current evidence that points to the place FET cycles will come to inhabit in the future. Safety issues have been central to the narrative around the clinical application of vitrification and, as the evidence base grows, the risk benefit balance will become clearer for different patient groups. These will include recipients of donor eggs, as in some centres the use of cryopreserved donor eggs now exceeds that of fresh oocytes. Efficient cryopreservation techniques have also affected international transport of gametes and embryos, increasing international access. The profound changes that vitrification has created promises to fulfil a prediction made by this journal's founding Editor, Bob Edwards, that embryo and cryopreservation would solve many of the challenges presented by assisted reproductive technology. Crown