Excess embryos of good quality that are not transferred can be cryopreserved (frozen). These embryos can be transferred into the uterus in a subsequent unstimulated cycle for another chance of pregnancy. 

Cryopreservation is a process whereby embryos may be frozen in a step-wise fashion using a computerised freezing process. These embryos are then stored in liquid nitrogen at -196 degrees Celsius for replacement in a subsequent treatment cycle (called a Free Thaw Cycle). Cryopreservation and later transfer of extra embryos give couples an additional chance to become pregnant following egg retrieval in an IVF/ICSI cycle.