Freezing or cryopreservation involves the storing of a patient’s samples in a special freezing medium in liquid nitrogen, which has an extremely low temperature of -196°C. Samples can then be kept frozen for many years before being thawed for a particular procedure. Frozen storage of embryos is restricted to five years by Australian law.
Egg freezing is a research procedure, which may give women the potential to have fertility treatment at a later date. This procedure is particularly relevant for women undergoing cancer treatments, women who might have medical conditions that are likely to affect their fertility or for women who wish to preserve their fertility for personal reasons. This is a relatively new procedure and success rates are uncertain. It is always preferable to store embryos rather than eggs if possible.
For oocyte freezing, the ovaries are stimulated with fertility drugs to produce a number of eggs. These are then frozen. When a woman wishes to become pregnant, the eggs are then thawed and fertilised using the ICSI technique.
Sperm freezing is a routine procedure.
Semen samples can be collected and frozen for future use. They are then thawed and prepared as for fresh semen samples. Freezing sperm does reduce the quality of sperm and sometimes intrauterine insemination is unsuccessful. There can be no guarantee of a successful pregnancy following sperm cryopreservation, however pregnancy rates using IVF or ICSI are in general excellent.
Good quality embryos are often frozen following IVF or ICSI procedures, where only one embryo is transferred. Thawed frozen embryos can then be used at a later date if treatment is unsuccessful or if a couple wish to have further children. Alternatively embryo freezing is a treatment option for women with a medical condition, which is likely to affect their fertility, or patients who have not been able to proceed with an embryo transfer after IVF or ICSI for some reason.
Click here for more information on frozen embryo transfer. If possible thawed frozen embryos are transferred during a woman’s natural cycle. However, women with irregular menstrual cycles may undergo hormone treatment to make the uterus more receptive to implantation.