What is embryo freezing?
The conventional IVF procedure, which utilizes fertility medications to stimulate ovulation, often results in many embryos. Since the risk of multiple pregnancies increases with the number of embryos transferred, many couple are left with more embryos than necessary or more embryos than can be transferred by law in some countries. In some countries, like the UK, the maximum number of embryos that can be transferred is three. These spare embryos can be discarded, used for research, or they can be frozen and cryopreserved for later use by the same couple or another couple wishing to use a donated embryo.
Who can benefit from frozen embryos?
Women who are at risk of developing ovarian hyperstimulation syndrome, following ovarian stimulation for IVF treatment, are advised to freeze all their embryos for consecutive transfer.
In some cases when fresh embryo transfer fails, “spare” embryos can be cryopreserved for a second or third trial.
Cryopreserved embryos are available for donation to barren couples. In fact, some countries mandate that all embryos resulting from donated eggs be cryopreserved and quarantined for a period of six months until all donor screening tests are complete.
Frozen embryos are just as good as fresh embryos, meaning that pregancy rates are just as high, and there is no more risk of abnormalities with frozen embryos than fresh, therefore patients are often encouraged to choose the more cost-effective route of freezing their embryos rather than discarding them, as a guarantee in the event that the first embryo transfer fails, or pregnancy is not carried out to term. Using frozen embryos, which can be stored for up to several years, is a much less expensive alternative to starting a new cycle.
How are the embryos frozen?
Embryos can be stored in batches of one or more. Like any living tissue, the cells of embryos contain water, which must be removed prior to freezing to prevent ice crystals from forming and causing the embryos to burst. The embryos are then gradually mixed with a cryoprotectant fluid that does not form ice crystals, and then put in a plastic straw or a glass ampoule. The mixture is stored in liquid nitrogen at a very low temperature using a specialized programmable machine. Temperature is crucial since embryos are subject to metabolic change.
Options may include the following:
- Freezing unfertilised eggs in an IVF cycle, instead of fertilising all eggs aspirated
- Disposal – although many clinics will not allow disposal of embryos created in their laboratories
- Placing the embryos back during the non-fertile part of a cycle – again, many clinics will not be open to performing this procedure
- Donation to Research, specifically for stem cell research
- Donation to another couple
- Freezing indefinitely, here you need to consider the annual cost of freezing the embryo/s at -196 degrees Celcius. With this option it is also important that you make provision for the fate of the embryos in the event of your, your partner or both your deaths. It is also wise to decide upfront what should happen to the embryos in the case of divorce.
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