Eggs, sperms, and embryos can be preserved for future use with the help of freezing or cryopreservation. The cryopreservation of the embryos is performed if they are to be preserved for transfer at a later date. Embryo cryopreservation would provide an additional opportunity for pregnancy by the process of Frozen Embryo Transfer or FET. The process by which freezing is done is called vitrification.
Freezing of embryos
The embryos that meet certain development criteria for their rate of growth and appearance can be frozen at different stages. The freezing process is controlled by a computer and special solutions are employed to protect these fertilized eggs. The eggs are generally stored at -400oF and would remain viable for a long period of time.
The survival rate of the frozen embryos is about 90-95%. The percentage of pregnancies that use cryopreserved embryos is quite similar to that using fresh embryos. No increase in the rate of spontaneous miscarriages or birth defects from pregnancies has been seen from the implantation of frozen embryos.
Freezing of sperms
Sperms can be cryopreserved, making them useful during the IVF or IUI cycles. This is used in those cases where donor sperms are used for fertilising the eggs. They are cryopreserved and quarantined for 6 months to ensure that they do not carry viral diseases.
Freezing of eggs
Freezing of eggs used to be considered to be an experimental condition until recently. This is because of the lack of proper data to predict the safety of unborn children. Earlier pregnancy rates with frozen eggs had been quite low. However, it has been seen that the children born from frozen eggs do not have any abnormalities. Vitrification, which is a special freezing technique, results in much higher pregnancy rates. Egg freezing can be used by women who wish to preserve their fertility.
How are the frozen eggs stored and monitored?
In the laboratories, there are large tanks filled with liquid nitrogen, where the embryos are stored. Each patient would have a designated storage space where the embryos would be kept. The straws containing the embryos are colour-coded and labelled with identifying information.
The tanks containing them are under constant monitoring. They go through daily physical inspections. The quantity of nitrogen is checked along with signs of leakage. Sensors are placed within the tanks to check temperature, pressure and other physical conditions.
How long can the embryos be stored?
The maximum storage period of embryos is not known. The procedures had been developed in 1984 and started being used widely in the late 1980s. Embryos have been awakened from their sleep even after 10-15 years to create healthy babies. It is possible that an embryo might be viable indefinitely if kept in liquid nitrogen.
How are embryos thawed?
The embryos coming out of the freezer are warmed to body temperature in about 2-3 seconds. The rapid thaw method minimizes damage to the embryos that could happen through the formation of ice. Now, the antifreeze has to be removed and the water has to be replaced. For this, the embryo is incubated in decreasing concentrations of antifreeze and increasing concentrations of water. The embryo is stepped through different solutions to that end.
The embryo would be ready for transfer in as little as 40 minutes.
Sperm or embryo freezing would depend on the requirements of the process being followed. The doctor would keep you updated through the entire journey.Authored by Dr. Radhika Meka
The doctor was very friendly. consultation was good and time was invested. This doctor was referred to me and I have been visiting her since 6 months and shall continue
doctor is very friendly. she explains clearly and is very supportive. the clinic is good and staff is trained. I have never faced and delay and she is quite punctual