Freeze-storage of embryos, known as cryopreservation, involves storing any surplus healthy embryos for future transfer.  The first “frozen embryo baby” was born in 1984.  Today some 60% of all patients having a stimulated cycle will have embryos frozen resulting in approximately 50% of all IVF births in our program.  

The advantage of embryo freezing is that it increases the chance of a pregnancy per stimulation cycle and egg collection without increasing the multiple pregnancy rate.  

For example, if six normal embryos were obtained in an IVF cycle we might suggest transferring one or two and freezing four or five embryos.  This would generally allow a further one or two embryo transfers in later cycles (or two embryos each), if pregnancy did not occur in the stimulated cycle.

Embryo storage is intended to be short term, however in Victoria it is possible to store embryos for up to five years.  Couples wishing to store embryos beyond this time are required to submit an application to the Infertility Treatment Authority for an extension.

Freezing technique
Embryos are placed in thin plastic straws, which are sealed at both ends and labelled with the name and identification number of the couple.  The straws are put into the freezing machine and the temperature is gradually reduced to -150 degrees celsius.  The straws are placed in goblets, which are then placed in tanks filled with liquid nitrogen, which keeps the temperature of the tank at -196 degrees Celsius.

Success rates from frozen embryos
At Melbourne IVF about half our births, over many years, have come from the transfer of frozen/thawed embryos. A thaw transfer is a much less complex and much less costly procedure than an egg retrieval cycle, yet these relatively easy cycles boost the birth rate significantly.

Success rates from frozen/thawed embryos are dependant on the age of the woman’s eggs when the embryos were frozen. This is where our model of care really makes a difference. If a 42-year-old woman uses frozen embryos, which, for example, were created at the time of her first pregnancy when she was 38, her fertility chance will be that of a 38-year-old woman, not a 42 year old.