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Why Freezing Your Embryos Has Never Been Safer

Thanks to new research, embryo cryopreservation is becoming more effective and error-resistant than ever.

July 9, 2021
Alexandra Ross

Scientists teaming up from across the world have announced exciting innovations in biotechnology this month, unveiling a new system to assist with embryo cryopreservation. Known more casually by some as freezing embryos, embryo cryopreservation is a process for storing fertilized embryos to be implanted at a later time. 

Embryo cryopreservation has been used by countless women to grow their families. With these new advancements, even more women will find success getting pregnant!

A female cancer patient, lying in bed with an IV in her arm, looking at a window out of frame
Many women who are diagnosed with cancer choose to preserve their eggs or embryos before beginning chemotherapy treatments. Chemotherapy can cause the loss of important hormones and cause premature or early menopause.

What is embryo cryopreservation?

Embryo cryopreservation is the process of fertilizing, freezing, and storing embryos for later use. It is often used as a part of in vitro fertilization (IVF) treatments, or for women who want to wait to get pregnant but are worried about their fertility prospects in the future — sometimes because they are going to receive medical treatments that harm their fertility.

Because cells are made up mostly of water, the freezing process must be meticulous to ensure that harmful ice crystals do not form inside or between the cells. Cryoprotective agents, also known as cryoprotectants, replace water in the embryos to ensure that ice does not form.

There are two forms of cryopreservation of embryos: slow freezing and vitrification. In slow freezing, the cryoprotectants are added more gradually, while vitrification is a faster and riskier technique. 

The embryos are frozen in liquid nitrogen at about -320 degrees Fahrenheit. They are thawed slowly when ready to be used, and the cryoprotectants are removed and replaced with water again to restore the cell to its natural state.

Why choose embryo cryopreservation?

Embryos can remain stored in liquid nitrogen for years after the cryopreservation process. This allows for greater flexibility and planning ability amongst women who are seeking to become pregnant.

Most women undergoing IVF treatments choose to use embryo cryopreservation, if multiple embryos are found to be viable. This is because IVF implantations are not always successful on the first try. The preservation of multiple embryos allows for the possibility of additional implantations, if necessary, without the need to undergo preparatory hormonal treatments more than once.

In March 2020, many fertility clinics offering IVF had to place a temporary halt on all IVF treatments due to COVID-19. Those who had already undergone the egg retrieval procedure, such as actress Amber Smith, kept their embryos preserved for months before they could return to clinics for implantation.

Another common reason for choosing embryo cryopreservation is because of a new treatment likely to impact fertility. Women who are diagnosed with cancer may need to undergo certain treatments, such as radiation or chemotherapy, that lower their chances of getting pregnant in the future. 

A pregnant woman holding her belly, the rest of her body out of frame.
Thanks to embryo cryopreservation, many women undergoing IVF treatments or who are impacted by medical treatments that reduce fertility are able to become pregnant. Advancements in embryo cryopreservation will help to bring this joy to more women than ever before.

An evolving practice

A new study, recently published in the journal Biomicrofluidics from AIP Publishing, reveals how scientists at the National Institute of Genetic Engineering and Biotechnology in Iran and MicGill University and the University of British Columbia in Canada have designed a new system for cryopreservation. This new system, based in microfluidics, automates parts of the process to reduce the likelihood of damage to the embryo.

What was the problem?

The process of removing water from the embryo and replacing it with cryoprotectants is the one of the most crucial and error-prone steps of cryopreservation. There are many risk factors to balance here — water left in the embryo can form damaging ice, but removing it too suddenly will kill the embryo; cryoprotectants need to eliminate the risk of ice forming, but these fluids themselves can be toxic if used in too-high concentrations. 

Usually, embryos are transferred through multiple droplets with varying and increasing concentrations of cryoprotectants in what is known as the slow freezing method. Embryos spend about 10-20 minutes in each of these droplets, and are transferred between them with pipettes. The multiple transfers of embryos opens up yet another opportunity for human error to damage the embryo.

Researchers knew there had to be a better way to implement this process, reducing the likelihood of error. They set out to find it. 

Schematic of the microfluidic platform for cryoprotectant loading. Graphic shows dimensions of 2cm X 6cm
A schematic of the microfluidic platform that National Institute of Genetic Engineering and Biotechnology, McGill University, and University of British Columbia researchers designed for automated and gradual cryoprotectant loading. This technology would reduce likelihood of damage to the embryo. Image courtesy of Phys.org.

What has changed?

“What if embryos simply stayed in the same place, and cryoprotectants were brought to them?”

This question, posed by National Institute of Genetic Engineering and Biotechnology assistant professor Mojtaba Dashtizad, was the foundation for the research that created this new microfluidics system. And why microfluidics? “Microfluidics systems are really good at controlling flow and concentration,” Dashtizad explained. 

In the new system, instead of going through multiple transfers and pipetting steps, an embryo is placed in a single chamber. Three channels gradually introduce cryoprotectants to the embryo as water is emptied out through a fourth channel. The concentration of cryoprotectants is automatically adjusted by the system, slowly and constantly increasing. 

“Our genetic studies show this reduces molecular damage caused by cryopreservation,” Dashtizad said. “And embryos can be cryopreserved faster and with a lower concentration of cryoprotectants — a huge advantage because of the toxicity of these chemicals.”

As a result, cryopreservation can be simpler, more reproducible, and more resistant to human error. Constant and gradual cryoprotectant concentration increases are safer for embryos than the sudden increases used in droplet-based methods. 

This microfluidics system will improve the quality of fertility treatments using embryo cryopreservation in the future, helping to raise the number of successful pregnancies through IVF treatments.

A close-up of a mother kissing her baby on the cheek. Background suggests they are outdoors.
Embryo cryopreservation is a crucial part of in vitro fertilization, which helps thousands of women to grow their families every year.

Embryo cryopreservation is an amazing scientific process that has helped so many women to get pregnant over the years. From fertility treatments such as IVF to medical treatments such as chemotherapy, there are many reasons why embryo cryopreservation may be an important part of your journey to pregnancy. 

In the past, the step of removing water from the embryo and replacing it with cryoprotectants has been susceptible to errors on several fronts. Thanks to the invention of this new microfluidic system, the human errors associated with the droplet method of embryo cryopreservation may be totally eliminated. 

As a result of this innovation, the embryo cryopreservation process will become even safer and more effective in the years to come, bringing even more women one step closer to getting pregnant!


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