Freezing (or Cryopreservation) of embryos is a common procedure. Since in a typical IVF cycle, multiple embryos are created and only one or 2 embryos are transferred into the uterus, there is sometimes a surplus of embryos. These embryos, if viable and of adequate quality, can be frozen for future use in a frozen embryo transfer (FET) cycle.
A FET offers significant cost savings in comparison to a fresh IVF cycle as the medications used to prepare the lining of the uterus are relatively inexpensive and the patient does not have to undergo an egg retrieval, which requires it to be performed in an operating room in the presence of an anesthesiologist. Furthermore, the availability of cryopreservation permits patients to transfer fewer embryos during a fresh cycle, reducing the risk of high-order multiple gestations (triplets or greater). Other possible reasons for cryopreservation of embryos include freezing all embryos in the initial cycle to prevent severe ovarian hyperstimulation syndrome (OHSS), or if a couple is concerned that their future fertility potential might be reduced due to necessary medical treatment (e.g., cancer therapy or surgery).
Overall pregnancy rates at the national level with frozen embryos are lower than with fresh embryos. This, at least in part, results from the routine selection of the best-looking embryos for fresh transfer, reserving the ‘second-best’ for freezing. There is some evidence that pregnancy rates are similar when there is no such selection.