Freezing & Thawing

Technically, there is no time limit on the storage of frozen eggs. Cryopreserved eggs have been successfully stored for decades and used to achieve pregnancy.

However, in Australia the various states and territories do have different laws for how long you can store your eggs.

What is Vitrification (Egg Freezing)?

Vitrification is a flash-freezing process used in cryopreservation to prevent the formation of ice crystals in biological cells, including human oocytes (eggs).

The technique is vital for preserving an eggs’ viability for future use in assisted reproductive technologies like in vitro fertilisation (IVF).

Vitrification has significantly improved the success rates of egg freezing by reducing the risk of ice crystal formation, which can damage the eggs.

Egg Freezing (Vitrification) Process:

The first step involves stimulating the ovaries with hormonal medications to encourage the production of multiple eggs. This process usually takes about 10-14 days.

Once the eggs are mature, they are retrieved from the ovaries using a minor surgical procedure. This is done under ultrasound guidance with a needle that aspirates the eggs from the follicles.

The retrieved eggs are then assessed under a microscope by embryologists. Only mature eggs are suitable for freezing, as they have the highest chance of surviving the freezing and thawing process.

Before freezing, the eggs are treated with a cryoprotectant solution. Cryoprotectants are substances that protect biological tissue from freeze damage (ice formation). The eggs are dehydrated to remove water and then exposed to increasing concentrations of cryoprotectants.

The eggs are rapidly cooled to a vitreous, or glass-like, state without forming ice crystals. This is achieved by placing the eggs in a tiny volume of solution on a special device or straw, which is then plunged directly into liquid nitrogen at a temperature of -196°C. The rapid cooling turns the water inside and around the egg into a solid state without forming ice crystals, which can damage the cell.

 The vitrified eggs are stored in liquid nitrogen until they are needed. They can be stored for many years without significant deterioration in quality.

 When the individual decides to use their frozen eggs, the eggs are rapidly warmed and the cryoprotectants are removed in a stepwise manner. The eggs can then be fertilised with sperm to create embryos, which may be transferred to the uterus to achieve pregnancy.

Not All Thawed Eggs Survive

Once you decide to use your frozen eggs, they must be safely thawed and prepared for use.

Approximate rates of loss of thawed eggs:

  • For a woman aged 35 or under, one stimulated cycle would result in the collection of about 10–15 eggs, of which 8–10 would be suitable for vitrification (freezing) and storage.
  • Approximately 70-90% of the eggs would survive warming (thawing) in the future.
  • Approximately 50-80% of surviving eggs would fertilise.
  • Approximately 50-90% of fertilised eggs would develop into embryos.
  • A single embryo would have a 20-35% chance of developing into a pregnancy.

Intracytoplasmic Sperm Injection (ICSI)

Intracytoplasmic sperm injection is a procedure used to inject a single sperm into an egg. Normally this procedure is only used for patients that have poor sperm quality and where we suspect that sperm may not be able to fertilise eggs on their own. However, due to the hardening of the zona that occurs with vitrification, all vitrified eggs are fertilised using the ICSI procedure. The changes in the zona prevent sperm from penetrating in the normal way, and each egg has to be individually injected with a single sperm.

Take the First Step

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