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Cryopreservation

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Embryo cryopreservation is the process of freezing fertilized eggs (embryos) so they can be stored and used in future fertility treatments.
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Cryopreservation

What is Embryo Cryopreservation ?

Embryo cryopreservation is the process of freezing fertilized eggs (embryos) so they can be stored and used in future fertility treatments such as IVF, without needing another round of egg retrieval and fertilization .This process is made possible through specialized methods that preserve embryos at extremely low temperatures.
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When is It Considered

Embryo cryopreservation is often chosen in several key situations:

  • Extra embryos from IVF : If more good-quality embryos are created during an IVF cycle than needed, the extras can be frozen for future attempts.
  • Fertility preservation : Individuals may freeze embryos before undergoing treatments like chemotherapy, radiation, or gender-affirming surgery, which could impact fertility.
  • Genetic testing : After IVF, embryos may be tested for genetic conditions. Cryopreservation allows time for these tests before transfer .
  • Freeze-all strategy : Sometimes transferring embryos immediately isn’t ideal—due to high hormone levels or health concerns—so all embryos are frozen and transferred later in a safer, more natural cycle .

Types of Cryopreservation

There are two main techniques to freeze embryos:

Vitrification (Flash Freezing)

  • Involves rapidly freezing the embryo after adding a protective liquid to prevent ice crystal formation.
  • This is now the preferred method due to its speed and high survival rates.

Slow Freezing

  • Involves gradually reducing temperature over time with smaller amounts of protective agents.
  • Less commonly used today, as it can cause more damage to cells.

Step Process

Process of Cryopreservation

A simplified outline of how embryo cryopreservation works:

Step 1 : Embryo Creation
  • Eggs are retrieved from the ovary and fertilized with sperm in the lab (IVF).
  • The embryos are nurtured for a few days, and high-quality ones are selected for freezing.
  • Selected embryos are treated with cryoprotectants (like antifreeze substances) and then frozen—usually with vitrification—into extremely cold liquid nitrogen (around –196 °C or –320 °F).
  • Frozen embryos are stored in secure, monitored tanks. Many clinics allow storage for years or even indefinitely .
  • When ready, the embryo is gradually warmed, protective agents are removed, and it's transferred into the uterus (either in a medicated or natural cycle).
  • Unused embryos can be discarded, donated to other couples, used for research, or allowed to perish according to legal and ethical consent agreements.

Results of Cryopreservation

  • High survival : Over 80% of embryos survive freezing and thawing; vitrification has pushed this even higher—sometimes over 95% .
  • Excellent long-term viability : Embryos can remain viable for decades—births have been reported from embryos frozen for 27+ and even 30 years .
  • Safe outcomes : Studies show no increased risk of birth defects or developmental problems in children born from frozen embryos .
  • Comparable success to fresh transfers : Pregnancy, implantation, and live birth rates are similar—and in some cases even better—than with fresh embryo transfers .