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The Embryologist's Role in Embryo Freezing (Cryopreservation)

The importance of the embryologist’s role in cryopreservation has grown with the rise in pre-implantation genetic testing and “freeze-all” strategies. Embryo cryopreservation and maintenance is considered to be a standalone sub-discipline of reproductive medicine. Embryo cryopreservation allows women undergoing IVF to have just ONE cycle, but continue to have embryos to use in the future. It helps to reduce the risk of Ovarian Hyperstimulation Syndrome (OHS), and allows for the endometrium to fully recover after ovarian stimulation.

History of Cryopreservation

The idea of maintaining the viability of living reproductive cells and tissues of various species and humans for long-term storage has been around for almost 50 years. Dr. Alan Trounson and Linda Mohr achieved the first human pregnancy from a frozen (8 cell) embryo in 1983 and the first live birth, baby Zoe, in 1984. In 2017, Emma Wren Gibson was born from an embryo that had been frozen for nearly 25 years - possibly the longest gap between conception and birth since IVF began.

Overall, embryo cryopreservation has decreased the number of fresh embryo transfers performed, and maximized the effectiveness of IVF cycles.

  • Data shows that women who had fresh and frozen embryo transfers obtained an 8% increase in additional births using cryopreserved embryos.

  • Randomized clinical trails (Coates 2017 and Magdi 2017) show that vitrification of blastocysts and frozen embryo transfer (FET) is superior.


Through efforts to constantly improve cryopreservation techniques, we are now able to preserve cells and tissues through a process called vitrification – transforming cells from a liquid state directly to a glass like state. This is done by replacing all the water in cells (dehydration) with a cryopreservation agent, and then by cooling the embryos to extremely low temperatures, such as −195.79°C (the boiling point of the liquid nitrogen). Cooling down biological objects to such degrees prevents any biological activity, including all the biochemical reactions involved in cell death!

Roles & Responsibilities of Embryologists

When cryopreservation methods fail, dreams and families are lost. Several high profile cases of liquid nitrogen storage failures, as well as the selection and transfer of the “wrong” embryo have been nightmare scenarios for the IVF industry. They highlight the embryologist’s important role in cryopreserving and storing embryos. Some of the roles and responsibilities of embryologists are:

  • To label, separate, and store embryos that are potentially infectious (for example, created with HIV+, Hepatitis + eggs or sperm) for use by a sexually intimate couple, for use by an unrelated gestational surrogate, or in cases of embryo adoption.

  • To understand embryo inheritance in cases of death, or use by either party in cases of separation and divorce.

  • To discard embryos that are genetically abnormal, or after individuals have completed building their families.

  • To collect and organize legal consents to store frozen embryos, to thaw embryos for transfer (or biopsy), or discard the tissues.

  • To correctly label, identify, and select embryos for transfer.

  • Maintain liquid nitrogen dewars at all times – over holidays and weekends- with optimal and adequate levels of freezing cold liquid nitrogen.

  • Detect environmental changes, inspect the condition of storage vessels, and, maintain alarm systems and liquid nitrogen gas supplies.

  • Ship (and receive) frozen embryos (and eggs and sperm) all around the world!


Guest Post by Dr. Carol Lynn Curchoe

Dr. Carol Lynn Curchoe, TS. is a reproductive biologist practicing clinical embryology. She's the founder of ART Compass, a mobile application for IVF Practice Management.

Her PhD. research focused on animal cloning at the University of Connecticut and her postdoctoral fellowship (The Burnham Institute) focused on human embryonic stem cell research.

Her active research interests span reproductive biology, from basic embryology to cutting edge artificial intelligence applications for IVF.


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