How Egg Storage Works: From Retrieval to Freezing

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Egg storage, from retrieval to freezing, involves several key steps to ensure the eggs are harvested, preserved, and stored correctly for future use. Here’s a detailed overview of the process:

1. Ovarian Stimulation

Before the eggs can be retrieved, the ovaries must be stimulated to produce multiple mature eggs which involves:

  • Hormonal Injections: The patient receives daily hormone injections for about 10-14 days. These hormones stimulate the ovaries to produce multiple follicles, each potentially containing an egg.
  • Monitoring: Regular ultrasounds and blood tests monitor the development of the follicles and hormone levels.

 2. Egg Retrieval

Once the follicles are ready, the eggs are retrieved via a minor surgical procedure involving:

  • Trigger Injection: A final hormone injection (trigger injection) is given to mature the eggs 36 hours before the retrieval.
  • Procedure: Egg retrieval is performed under sedation or anaesthesia using an ultrasound-guided needle. The needle withdraws the fluid from the follicles to collect the eggs. The procedure typically takes around 15-20 minutes.

3. Identification and Assessment

The retrieved fluid is examined to identify and assess the eggs.

  • Laboratory Examination: The fluid is handed over to an embryologist who identifies and isolates the eggs.
  • Assessment: The eggs are assessed and the mature eggs (in metaphase II) are chosen for freezing.

4. Freezing (Vitrification)

The identified mature eggs are then prepared for freezing through a process called vitrification, read more here.

  • Cryoprotectants: Eggs are exposed to cryoprotectants to protect them from ice crystal formation during freezing.
  • Vitrification: The eggs are rapidly cooled to a sub-zero temperature using liquid nitrogen.


5. Egg Storage and Monitoring

The frozen eggs are stored securely and monitored until they are needed for future use. 

  • Egg Storage Tanks:  Vitrified eggs are stored in liquid nitrogen tanks at temperatures of around -196°C

6. Thawing and Frozen Embryo Transfer (FET)

When the patient is ready to use the frozen eggs, the eggs are thawed and fertilised.

  • Thawing Process: Eggs are carefully warmed and rehydrated to reverse the vitrification process.
  • Fertilisation: Thawed eggs are fertilised by injecting a single sperm into each egg.
  • Embryo Transfer: One or more embryos are transferred to the patient’s uterus in hopes of achieving pregnancy, learn about how to prepare for FET here.  

Improving the health and quality of your eggs is really important for egg retrieval and freezing as it increases your chances of success fertilisation.

Zita West offers a free webinar on how to boost egg quality and offers an additional Ultimate Egg Health Pack, containing all the supplements we recommend for supporting egg health. To learn more about boosting egg health, read here


Further reading

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