The Science Behind Freezing Embryos: Freezing your Embryos and how does it work?

May 2, 2024
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Embryo freezing, also known as cryopreservation, is a remarkable scientific technique that allows individuals or couples to preserve their embryos for future use. This process has revolutionized assisted reproductive technologies, providing hope for those facing fertility challenges or individuals who wish to delay starting a family. In this blog post, we will delve into the fascinating world of embryo freezing, exploring the science behind it and how the process works.

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I. Understanding Embryo Cryopreservation

Embryo cryopreservation involves freezing and storing embryos at ultra-low temperatures, typically around -196°C (-321°F), in liquid nitrogen. This process halts all biological activity, effectively preserving the embryos' viability for an extended period. The technique is commonly used in conjunction with In-vitro Fertilization (IVF) treatments.

II. Preparing Embryos for Cryopreservation

Before embryos can be frozen, certain steps are taken to optimize their chances of survival. These include:

  • Controlled Ovarian Stimulation: The woman undergoing IVF treatment receives hormonal medications to stimulate her ovaries, resulting in the development of multiple mature eggs.
  • Egg Retrieval: The eggs are surgically retrieved from the woman's ovaries using ultrasound guidance and a fine needle.
  • Fertilization: In the laboratory, the retrieved eggs are fertilized with sperm, either through traditional IVF or Intracytoplasmic Sperm Injection (ICSI).
  • Embryo Development: The resulting embryos are cultured in a laboratory incubator for several days, allowing them to reach a suitable stage for cryopreservation, typically at the blastocyst stage.

III. The Cryopreservation Process

Once the embryos have reached the desired developmental stage, they are ready for cryopreservation. The process involves several key steps:

a) Dehydration: Embryos are exposed to a cryoprotectant solution to protect them from ice crystal formation during freezing. This solution replaces the water inside the embryos, preventing potential damage.

b) Vitrification: The embryos, now dehydrated, are carefully placed in small containers, such as cryotubes or straws. These containers are rapidly immersed in liquid nitrogen, causing the formation of a glass-like solid called a vitrified state. Vitrification reduces the risk of ice crystal formation and associated damage to the embryos.

c) Storage: The vitrified embryos are transferred to long-term storage tanks filled with liquid nitrogen, where they can remain indefinitely. These tanks are specifically designed to maintain extremely low temperatures, ensuring the embryos' preservation.

IV. Thawing and Transferring Frozen Embryos

When individuals or couples are ready to use their frozen embryos, the thawing process begins. This involves:

  • Removing the embryos from storage: The desired number of embryos is carefully retrieved from the storage tank.
  • Rapid warming: The embryos are quickly exposed to a warming solution to rapidly rehydrate them and remove the cryoprotectant.
  • Assessing viability: The thawed embryos are evaluated for survival and potential damage. The viable embryos are then selected for transfer to the woman's uterus.
  • Embryo transfer: The selected embryos are transferred into the woman's uterus using a thin catheter. The embryos will hopefully implant and result in a successful pregnancy.


Embryo freezing has revolutionized the field of reproductive medicine, providing hope and options for individuals and couples facing fertility challenges. Through the process of cryopreservation, embryos can be preserved and stored for future use. Understanding the science behind embryo freezing allows individuals to make informed decisions and explore this remarkable technology as they embark on their journey towards building a family.