Medical grounds for storing frozen fertilised eggs
- For later transfer of surplus embryos from various IVF treatment.
- For transferring the fertilised eggs in a later cycle than the actual IVF cycle, if unforeseen events occur such as illness in the woman or imminent overstimulation before the transfer, which must therefore be postponed or cancelled.
- In order for embryos to be studied for serious congenital defects before transfer – especially if the parents have serious congenital disorders.
- With a view to later fertility treatment if the man or woman is to have chemotherapy or radiation therapy, which will result in sterility.
- With a view to possible donation to another couple (not permitted in Denmark).
- For research purposes.
Freezing and thawing of fertilised eggs.
FER (Frozen Embryo Replacement).
As a rule, only two good fertilised eggs are replaced in the uterus with “fresh” IVF treatment. If more additional good fertilised eggs are present, they can be frozen at -190o C and stored in liquid nitrogen at this temperature for as long as necessary, although in Denmark the eggs must be destroyed no later than five years subsequently.
The “surplus” embryos can be thawed at a later date with a view to transfer e.g. in a natural cycle without hormone treatment. If only the best pre-embryos are frozen, the chances of the eggs surviving the freezing and thawing process will be reasonably good e.g. 50-75% will survive. When we have thawed the eggs, we wait for 24 hours before transferring them to the uterus in order to determine the eggs that can continue growing and further developing.
The eggs do not improve from being frozen and, as the chances of pregnancy with the freeze/thaw treatment are somewhat lower than with fresh IVF, we often transfer three thawed eggs. However, in many cases, only two eggs are transferred when considered expedient and otherwise possible.
This increases the chances of pregnancy without appearing to increase the risk of multiple pregnancies.
When transferring eggs in a natural cycle, ultrasound scans are conducted and blood tests are carried out to optimise the chances of pregnancy. Thawing can always be postponed if there is the least doubt about the quality of the cycle.
In these situations, women can also be given hormone treatment, when most practical, especially those who do not have normal ovulation.
Ilselil og Louise
