Intended Parents

The Embryo Thawing Process

Embryos can be frozen to preserve fertility. Embryo thawing is a step that must be taken when using frozen embryos for IVF or surrogacy.

If freezing embryos is right for your journey, learning about the embryo thawing process can reassure you about the safety of your embryos.

Contact us online to learn more about your fertility options if you need to have your embryos frozen. Having embryos going into an option such as surrogacy allows you to be matched with a surrogate that much quicker.

Below, we’ll look at why embryos are frozen and then thawed, the steps to the embryo thawing process and how successful those embryos are after being thawed.

What is Embryo Thawing?

Embryo thawing is the process of warming frozen embryos and replacing the cryoprotectant agent used to preserve them at -196ºC with water. This restores their biological activity.

In-vitro fertilization (IVF) produces multiple embryos but not all of those embryos will be used. The remaining embryos can be donated to another family looking to grow, donated to science, disposed of or frozen for later use.

This allows intended parents to preserve viable embryos for future attempts at pregnancy, whether due to health concerns, personal circumstances or the desire to have additional children later.

Embryo Thawing Process [5 Steps]

The embryo thawing process will depend on the specifics of your circumstances. Meet with your fertility specialist to discuss the thawing procedure and any specific protocols. Plan the thawing process according to your cycle, ensuring the timing aligns with your uterine receptivity.

5 General Steps to the Embryo Thawing Process

The embryos will be carefully removed from the cryogenic storage tank.

Then, the embryos will be placed in a pre-heated thawing solution warmed to the appropriate temperature (typically around 37°C).

Gradual rehydration involves transferring the embryos through a series of solutions to gradually rehydrate them by replacing the cryoprotectant agent (substance used in freezing) with water.

A microscope will be used to assess the appearance and viability of the embryo after embryo thawing. Your fertility specialist will be looking for cell integrity and the presence of any fragmentation while noting the condition of each embryo.

Based on their assessment, they’ll select the most viable embryos for transfer, while also grading cell quality and where the embryo is at in the developmental stage.

If you are curious about your chances of success after thawing you can learn more about frozen embryo transfer success rates and what you can expect during the next steps in your fertility journey.

When Do They Thaw Embryos for Transfer?

Timing matters. Embryo thawing typically takes place a few hours before the frozen embryo transfer.

If the embryo thawing process takes place too early, the embryo could grow incongruously with the uterine lining.

How Long Does It Take to Thaw an Embryo?

The process for embryo thawing is fairly quick. The thawing itself may take around 15 minutes or so but all told, you may be looking at one to two hours total. Beyond the 15 minutes, you need to factor in time that is required for warming, rehydration and assessment.

Do Embryos Survive Thawing?

Yes, most embryos that are thawed survive. According to John Hopkins Medicine, over 95% of frozen embryos survive the thawing process.

The survival rate is dependent on:

Vitrification has become the go to method for freezing embryos as they tend to have higher survival rates compared to slow freezing methods.

Embryo quality at the time of vitrifciation can impact its ability to survive the embryo thawing.

Following a standardized and precise thawing protocol ensures the best possible outcome for the embryos.

A high survival rate for the thawed embryos does not equate to the chances of a pregnancy. That is dependent on several factors, with age being a big one.

Procedures using eggs from women age 35 or younger have the highest chances in resulting in a pregnancy.

Can a Thawed Embryo be Frozen Again?

Yes, frozen embryos can be thawed and refrozen. This can be done with embryos at any developmental stage, from zygotes to blastocysts. In fact, it’s not uncommon for frozen embryos to be thawed for examination. It’s routinely performed with over 90% success.

What Are the Risks of Embryo Thawing?

Freezing embryos can damage them and so can the embryo thawing process. Depending on how many embryos are frozen, some or all of them may not survive.

But overall, it’s a safe process with high chances of survival from many reputable institutions such as Johns Hopkins Medicine (95%) and the National Library of Medicine (93.86%).

Does Embryo Quality Change After Thawing?

Yes, embryo quality changes after thawing. Once thawed, embryos will re-expand to the stage of development they were at before freezing, but embryo thawing can affect an embryos grade, shape, ability to re-expand and its chances of success with the embryo transfer.

If you intend to freeze your embryos for IVF or surrogacy, we can help you find a clinic. Fill out our online contact form to get recommendations for reputable fertility professionals near you.