Embryos, eggs and sperm can be preserved for future use by cryopreservation (freezing).
Cryopreservation of embryos is often used when there are more embryos than needed for a fresh IVF transfer. Embryo cryopreservation can provide an additional opportunity for pregnancy, through Frozen Embryo Transfer (FET), without undergoing another ovarian stimulation and retrieval.
Embryos that meet developmental criteria for appearance and rate of growth can be frozen at any of several stages in their development. The freezing process is computer controlled and employs special solutions to protect the fertilized eggs from damage. Frozen embryos are stored at approximately -400°F and can remain viable for long periods of time.
The survival rate of frozen embryos is now 90 to 95 percent. In addition, the rate of pregnancy using cryopreserved embryos is similar to the rate when using fresh embryos. There is no known increase in the rate of spontaneous miscarriages or in the rate of birth defects from pregnancies that have resulted from the implantation of previously frozen and thawed embryos.
Sperm can be cryopreserved and stored for use during an IUI or IVF cycle. All donor sperm is cryopreserved and quarantined for a period of six months to confirm that the donor does not carry any viral diseases. As with embryos, some sperm do not survive cryopreservation and thawing.
Until recently, egg freezing was considered an experimental treatment. This was because there was not enough data to predict if there would be harm to children born through this method and because earlier pregnancy rates using frozen eggs were quite low. Thus far, the data suggest children born from frozen eggs have turned out fine. They also suggest that using vitrification (a specialized freezing technique) for egg freezing results in much higher pregnancy rates—similar to those of IVF treatment. Egg freezing is often used by women wishing to preserve their fertility and family building options.