What Is Vitrification? How Does It Work?
- Until recently, the only method for freezing oocytes (or unfertilized eggs) was a slow-freezing method. This worked okay for freezing sperm or embryos. However, for eggs, the slow freeze process had many problems.
- Ice crystals were a major issue. Eggs contain a lot of water, compared to sperm and even embryos. Freezing eggs led to crystal formation. These crystals broke down the egg.
- To help minimize the number of ice crystals, scientists would remove some of the water. But it's impossible to remove all the water.
- When the eggs were thawed, they were damaged and frequently unusable. Fertilization and pregnancy rates for these slow-frozen eggs were low.
- With vitrification, the freezing process is so fast that ice crystals don’t have a chance to form. Vitrification has made egg freezing a much more viable option for women.
- Vitrification is also being used for embryo and sperm cryopreservation. Research is ongoing, but so far, pregnancy rates seem higher with vitrification, according to a 2014 study.
How Does Vitrification of Eggs Work?
- Vitrification of eggs requires high concentrations of cryopreservants, or an anti-freeze substance. Because anti-freeze is potentially toxic to the egg, the technique requires special care.
- The oocyte is first placed in a bath with a lower concentration anti-freeze. The solution also contains some sucrose, or sugar, to help draw water out of the egg. Next, the egg is placed in a highly concentrated bath of anti-freeze for less than one minute, while being instantaneously frozen.
- The eggs can then be stored in special cryogenic freezers, made for this purpose. The eggs are held in tiny straws.
- When it's time to thaw the egg, the oocyte must be warmed quickly and removed from the solution immediately.
- Once thawed, the egg can be fertilized using IVF with ICSI. ICSI involves taking a single sperm and injecting it directing into the egg. Regular IVF isn’t possible because the freezing process hardens the eggs outer membrane.