The main benefit of freezing embryos is that they can be transferred in later treatment cycles without the need for further ovarian stimulation or egg collection. Not all embryos survive the freezing and thawing process however and the success of this treatment might not be as good as when using fresh embryos.
There are different methods of preparation for FER.
Ultrasound scans are used to monitor the FER cycle. The embryos are then thawed and replaced into the uterus at the same stage in the cycle as when they were frozen.