Understanding The Thawing and Fertilisation Process: After Egg Freezing: The Thawing and Fertilisation Process

Egg freezing involves several steps, from ovarian stimulation and egg retrieval to cryopreservation. But once your eggs are safely frozen, what happens next? This module focuses on thawing and fertilisation, the key steps when you’re ready to pursue pregnancy.

To learn more about the earlier stages of egg freezing, explore our other modules, such as Introduction to Egg Freezing, Who Is Egg Freezing For, and many more.

Thawing is the process of gently warming frozen eggs to a temperature that allows them to return to a viable state for fertilisation. When you decide to use your frozen eggs, your fertility specialists will begin the thawing process on the selected egg.

This step is done carefully to avoid damage to the eggs, particularly from ice crystals that may have formed during freezing.

Fertilisation occurs when a sperm from the father and an egg from the mother join together to form an embryo.

This can happen naturally or via assisted reproductive technology (ART), which we’ll explore in the next chapter.

Egg quality naturally declines with age. As a result, the number of frozen eggs needed to achieve a higher chance of pregnancy increases with age.

Studies suggest freezing about 7 eggs for women under 30, 11 eggs for women aged 30-35, 23 eggs for women aged 36-40, and around 43 eggs for women over 40 to reach a 95% cumulative chance of pregnancy.

However, everybody is different. It's best to speak with your fertility specialist for a more personalised estimate of how many eggs you may need to freeze based on your age, fertility profile, and family planning goals.

Thanks to advanced vitrification techniques, frozen eggs can be stored for years while maintaining their viability. However, not all eggs survive the thawing process.

Survival rates typically range from 70% to 90%, depending largely on the woman’s age at the time of egg retrieval. Eggs collected at a younger age tend to tolerate freezing and thawing better.

The fertilisation rate of thawed eggs typically ranges from 71% to 79%. This rate depends largely on the age of the woman at the time the eggs were retrieved. Eggs frozen at a younger age generally have a higher chance of successful fertilisation, while those retrieved later in life tend to have lower rates.

Sperm quality also plays a key role, so both egg and sperm factors should be considered when planning treatment.

Pregnancy success using frozen eggs depends on two key factors: the age at which the eggs were frozen and the age of the woman at the time of embryo transfer.

As mentioned earlier, eggs frozen at a younger age tend to have higher fertilisation success due to better quality. However, the woman’s age at the time of transfer also matters. Those under 30 have about a 50% chance of pregnancy success, while those over 40 see rates closer to 21%.

Understanding these factors and consulting a fertility specialist can help you make informed decisions.