During an IVF/ICSI treatment cycle the eggs collected from the woman’s ovaries will be fertilised using her partner’s/donor sperm. Those fertilised eggs will be cultured in a specialised incubator to allow their development into embryos.
Usually the best quality embryo is transferred back into the woman’s uterus 3 or 5 days later. When there is a surplus of good quality embryos remaining these can be selected for cryopreservation (freezing).
Embryo freezing (cryopreservation) is a method of preserving the viability of embryos by carefully cooling them to very low temperatures using a rapid freezing process called vitrification. This involves freezing the embryo about 600 times faster than the traditional slow rate freezing, resulting in better embryo survival and quality after thawing. Cryopreserved embryos are preserved in liquid nitrogen for future use.
What are the benefits of embryo freezing?
The benefit of embryo freezing is that a good quality embryo is kept for use in a future frozen embryo transfer cycle. This means for example, that if a couple have a baby from an IVF or ICSI cycle and wish to have a sibling, they do not need to undergo the IVF (ovarian stimulation and egg collection) process all over again. Similarly, if the first cycle is unsuccessful they can opt to use the frozen embryo rather than going through IVF treatment cycle.
Some couples will have several embryos frozen and therefore enough frozen embryos for more than one subsequent cycle.
It is also a method of fertility preservation due to the fact that the embryo is frozen at a younger age when the woman’s egg, and resulting embryo quality, may be at its best.
What does a frozen embryo transfer cycle involve?
Frozen embryo transfer cycles are relatively simple. Most commonly, the woman takes hormone tablets to prepare the endometrium (lining of the womb). The process is monitored by transvaginal ultrasound scans to identify when the embryo transfer should take place.
On the day of embryo transfer, the embryo is carefully thawed and reassessed for its quality. The process of transferring the embryo is similar to a smear test and does not require sedation. A fine catheter (tube) containing the embryo is carefully inserted into the uterus under ultrasound guidance. The embryo is then placed in the uterine cavity.
Two weeks later a pregnancy test is taken at home.
How successful is frozen embryo transfer?
As only good quality embryos are selected for freezing, a frozen embryo transfer has approximately a 50% chance of having a baby. However, the chance of success depends on the quality of the individual embryo.
With the introduction of vitrification frozen embryo transfers have comparable pregnancy rates to fresh embryo transfer.
Are there any disadvantages to embryo freezing?
Approximately 80% of the embryos that are frozen will survive the thawing process. This does vary between patients and it’s possible that none of the embryos will survive the freezing and thawing process.
However, if there is a surplus of good quality embryos after IVF/ICSI cycles it’s recommended you consider embryo freezing. This is because it has a very high chance of success.