What is the difference between Egg Freezing and Embryo Freezing?

Egg freezing and embryo freezing are two different methods of fertility preservation commonly used in assisted reproductive technologies. While they share the common goal of preserving fertility, they differ in the stage at which the reproductive material is frozen and the implications they have for future fertility treatments. 

In this blog, we explore the differences between egg freezing and embryo freezing in more detail.

 

Egg Freezing: 

Egg freezing, also known as oocyte cryopreservation, involves the extraction and freezing of a woman's eggs for later use. This procedure allows women to preserve their eggs when they are at a younger age and have better fertility potential. Egg freezing is typically pursued by women who are not yet ready to start a family but want to preserve their fertility due to medical reasons, career goals, or personal circumstances.

The process of egg freezing begins with hormonal stimulation to encourage the ovaries to produce multiple eggs instead of the usual single egg that is released each month during a natural menstrual cycle. This is done through the administration of fertility drugs, usually in the form of injections. During this time, the woman's hormone levels and egg development are closely monitored using ultrasound scans and blood tests.

Once the eggs have matured, they are retrieved using a minimally invasive procedure called transvaginal ultrasound-guided follicle aspiration. A thin needle is inserted into the ovaries, and the eggs are carefully suctioned out. The retrieved eggs are then rapidly cooled and frozen using a process called vitrification, which involves ultra-rapid freezing to prevent the formation of ice crystals that can damage the eggs. The frozen eggs are stored in a cryopreservation facility until the woman decides to use them.

 

Embryo Freezing: 

Embryo freezing, also known as embryo cryopreservation, involves the freezing of embryos created through in vitro fertilization (IVF) for later use. IVF is a process where eggs are fertilized with sperm in a laboratory setting. The resulting embryos are then allowed to develop and monitored by an Embryologist for a few days before being frozen.

The process of embryo freezing begins with ovarian stimulation, similar to egg freezing, to produce multiple mature eggs. These eggs are then retrieved through transvaginal ultrasound-guided follicle aspiration. However, instead of freezing the eggs individually, they are fertilized with sperm in the laboratory to create embryos.

After fertilisation, the embryos are cultured in a laboratory for a few days to allow them to develop and reach a certain stage of maturity. The typical stages at which embryos are frozen are either at the cleavage stage (around day 2-3), or the blastocyst stage (around day 5-6). The choice of freezing at the cleavage or blastocyst stage depends on various factors, including the woman's age, the quality of the embryos, and the recommendations of your  fertility specialist.

Once the embryos have reached the desired stage of development, they are cryopreserved using the same vitrification process as egg freezing. The frozen embryos are stored in specialised containers and can be stored for extended periods, up to 55 years in the UK with 10 yearly re-consent forms, until the individuals or couples are ready to use them. 

 

Differences between Egg Freezing and Embryo Freezing:

• Timing: The main difference between egg freezing and embryo freezing lies in the timing of freezing. Egg freezing involves freezing eggs before they are fertilized, while embryo freezing involves freezing embryos after fertilization has occurred.
  
  
• Ownership and decision-making: Egg freezing provides individual women with the opportunity to preserve their fertility without the need for a partner or a sperm donor. The decision to use the frozen eggs in the future, either for pregnancy or for research purposes, rests solely with the woman. In contrast, embryo freezing requires sperm from a partner or a sperm donor, and decisions regarding the use of the frozen embryos must be made jointly by the couple.
  
  
• Success rates: Embryo freezing generally has higher success rates compared to egg freezing. This is because embryos have already undergone the process of fertilization and are at a more advanced stage of development, making it easier to select the most viable embryos for transfer during a future IVF cycle. In egg freezing, the eggs are frozen before fertilisation, and their viability can only be determined after they are thawed, fertilised, and allowed to develop into embryos.
  
  
• Ethical and legal considerations: Embryo freezing raises ethical and legal questions regarding the status of the embryo and the disposition of unused embryos. In some cases, there are restrictions and regulations surrounding the freezing, storage, and disposal of embryos, should a couple part ways. Egg freezing, on the other hand, does not involve the same ethical and legal complexities since the eggs are not yet fertilised and remain the property of one individual.
  
  
• Flexibility: Egg freezing provides women with the flexibility to choose their partners or sperm donors in the future. It also allows them to undergo fertility treatments at a later stage while still using their own eggs. In contrast, embryo freezing requires a committed partner, or a chosen sperm donor at the time of freezing, as the eggs have already been fertilized.

In summary, while both egg freezing and embryo freezing are methods of fertility preservation, they differ in terms of the stage at which the reproductive material is frozen, ownership and decision-making, success rates, ethical and legal considerations, and flexibility for future fertility treatments. These differences make each option suitable for different individuals based on their specific circumstances and reproductive goals.

It is important for individuals considering fertility preservation to consult with a fertility specialist, such as our own Dr Irfana Koita, who can provide personalised guidance and discuss the most appropriate option based on your unique situation.

 

Book a Consultation with Dr Koita.

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