Embryo banking uses the process known as cryopreservation (freezing) to temporarily preserve fertilized human eggs for a future pregnancy. Healthy eggs are harvested from the ovaries and are then fertilized with selected sperm in a laboratory. The resulting embryos (aka blastocysts) are then frozen – or “banked” – for storage.
Freezing and Storing Embryos
In 1984, human embryos were successfully frozen for the first time. Today, embryo freezing is a routine part of the IVF process. Over 60% of infertility patients decide to bank embryos, and hundreds of thousands of babies have been born thanks to this innovation. Pregnancy rates with frozen/thawed embryos are about as good as pregnancy rates for embryos that were transferred fresh (i.e., without ever being frozen).
Frozen embryo transfers have allowed many patients to achieve more than one pregnancy from a single cycle of ovarian stimulation. If the initial fresh (non-frozen) embryo transfer attempt does not result in a sustainable pregnancy, embryo cryopreservation provides patients with more chances. Not having to begin an entirely new IVF cycle reduces the cost. Another added benefit is that fewer medications are administered to the patient, and stress is reduced to some degree.
In the past, in order to increase the chances of pregnancy, many fresh embryos would be placed into the uterus at once. The hope was that at least one would attach and grow, without the need to repeat the delicate, expensive, time-consuming and often frustrating process. A frequent side effect was high-order multiple births (e.g., triplets or more). By freezing several good-quality embryos at the same time for future use, fewer need to be placed in the uterus during each cycle, which reduces the likelihood of high-order multiple births.
Embryos can be frozen at any stage of development during the IVF process, as soon as one day following the egg retrieval procedure. However, they are usually allowed to develop for a number of days, to ensure viability.
Fertilization through IVF: Eggs can be fertilized to form an embryo through in vitro fertilization and/or ICSI (intracytoplasmic sperm injection) – which requires only a single sperm to be introduced directly to the egg.
Storage: Embryo freezing, or embryo cryopreservation, is the last step in the process. Vitrification is a fast method of cryopreservation resulting in high survival rates. The embryos are bathed in a special solution and placed in special freezer which is surrounded by liquid nitrogen. This step is tricky, as care must be taken to avoid the formation of ice crystals (which might damage the cells).
Properly frozen embryos can be safely stored for years. The embryos tolerate freezing quite well, with over 90% surviving the process.