Fresh vs. Frozen Embryo Transfer: What You Need to Know

The choice between fresh and frozen embryo transfer is a key decision in the IVF process. While both approaches have proven successful, recent research shows shifting success rates and evolving recommendations. This article looks at the differences between fresh and frozen transfers, their respective benefits and limitations, and how to determine which option might be right for you.

What's the difference between a fresh and frozen embryo transfer?

During IVF, fertility medications help the ovaries produce multiple eggs, which are then retrieved and fertilized with sperm in a laboratory. Over several days, these fertilized eggs develop into embryos, growing from a single cell to a complex structure of hundreds of cells called a blastocyst. At this point, your doctor will either proceed with a fresh transfer of the embryo to your uterus (or the uterus of a gestational carrier) or freeze the embryos for a later transfer.

In a fresh embryo transfer, the embryo is transferred to the uterus immediately after fertilization and development in the lab, typically 3-5 days after egg retrieval. The process aligns with your natural cycle and the hormonal stimulation used for egg retrieval.

Frozen embryo transfer (FET), on the other hand, involves freezing embryos immediately after they reach the blastocyst stage. They're then thawed and transferred in a subsequent cycle, which can be weeks or years later. This allows families the chance to do genetic testing on the embryos. 

Can you do a fresh embryo transfer from frozen eggs?

Yes, you can do a fresh embryo transfer using frozen eggs. This is common when working with frozen donor eggs or when using your own previously frozen eggs. In this scenario, the frozen eggs are thawed and fertilized with sperm. The resulting embryos are cultured in the lab and transferred to the uterus without ever being frozen. This is considered a fresh embryo transfer because the embryo itself was never frozen, even though the eggs started out frozen.

How we define “fresh” vs. “frozen” transfers can be confusing. The "fresh vs. frozen" designation refers specifically to whether the embryo was frozen, not the eggs or sperm used to create it. 

Here's a simple way to think about it:

• If the embryo was frozen at any point before transfer = Frozen embryo transfer
• If the embryo was never frozen before transfer = Fresh embryo transfer

This classification stays the same whether you're using fresh or frozen eggs, donor or own eggs, or fresh or frozen sperm. The key factor is whether the embryo itself was frozen.

When using frozen eggs, you have two main options:

1. Thaw the eggs, create embryos, freeze them, and transfer in a subsequent cycle
2. Synchronize the egg thawing with either a natural or medicated cycle, allowing embryo transfer without an additional freeze

The key factor in determining your approach will be the synchronization of embryo development with optimal endometrial receptivity, which your clinic will carefully plan based on your specific circumstances.

Success rates between fresh and frozen embryo transfers

A clinical study from 2024 looked at whether there's any real difference between doing a fresh embryo transfer versus freezing all embryos and doing a frozen transfer later. They specifically looked at cases where genetic testing (PGT-A) of the embryos wasn't done, studying over 8,000 patients having their first IVF transfer.

The key finding was simple: both approaches worked equally well. Live birth rates were about the same - 44% for fresh transfers and 46% for frozen transfers. This held true across different age groups and even when patients had different levels of estrogen during their IVF cycles.

The researchers concluded that doctors and patients can choose either approach for a first IVF cycle. However, they note that certain situations might still favor freezing all embryos, like when there's a risk of ovarian hyperstimulation syndrome (OHSS) or when hormone levels aren't optimal. The choice should be based on each patient's specific situation after a thorough discussion with their doctor.

An interesting point about cost was mentioned too - different healthcare systems saw different cost implications. In some places, fresh transfers were more economical, while in others, the frozen approach made more financial sense.

However, ethnicity may play a role in outcomes. In 2016, I wrote a paper comparing South Asian and Caucasian women undergoing frozen embryo transfers and found interesting differences. While first-time frozen transfer cycles showed similar success rates (43% live birth rate for both groups), South Asian women who had previously undergone fresh transfers had significantly lower live birth rates compared to Caucasian women (21% vs. 37%). The study included 196 Caucasian and 117 South Asian women, with South Asian women being generally younger (34.9 vs. 37.1 years) and more likely to be nulliparous (59% vs. 43%).

Benefits of frozen embryo transfer

• Time for genetic testing: A frozen transfer allows time for preimplantation genetic testing (PGT), which can screen embryos for chromosomal abnormalities before transfer.
• Lower risk of OHSS: Ovarian hyperstimulation syndrome is a potential complication of fertility medications. Although today the overall risk is very low, if you are both the one retrieving eggs and having embryos transferred to your uterus, doing a FET can reduce this risk.
• Scheduling flexibility: You can plan the transfer around your schedule, and take time to prepare your body optimally for pregnancy.
• Storage for future family building: Extra embryos can be stored for future transfers if you want more children later.

Benefits of fresh embryo transfer

• Faster timeline: Since there's no waiting period between egg retrieval and transfer, you could potentially achieve pregnancy sooner.
• Lower initial costs: Without freezing and storage fees, the upfront costs are typically lower.
• Fewer procedures: The embryo doesn't go through the freeze-thaw process, which some patients prefer.
• Slightly better outcomes: Research has shown that for some people with diminished ovarian reserve, fresh embryo transfer may be beneficial. However, for most people, frozen embryo transfer outcomes are better.

Questions to ask your doctor

This decision shouldn't be made alone. Your doctor knows your specific medical history, test results, and circumstances. They can help guide you toward the option that makes the most sense for your situation. What works best for one patient might not be ideal for another, which is why it's important to have an open discussion with your healthcare team about your specific case.

To make an informed decision, consider asking:

• Based on my age and health history, which approach do you recommend?
• What are my personal success rates likely to be with each method?
• How might my hormone levels affect success rates?
• What are the cost differences for my specific situation?
• If we choose fresh transfer, can we freeze any remaining embryos?
• What's your clinic's success rate with each method?

Making your decision

While we outlined various factors that might influence the choice between fresh and frozen transfer, it's important to remember one key point: The research shows that both approaches work well, with very similar success rates. This means that of all the many decisions you'll face during your fertility journey, this isn't one you need to stress about - both paths can lead to success.

The decision between the two approaches should be based on medical evidence, personal circumstances, and careful consultation with your fertility clinic. As technology advances and success rates continue to improve, both options remain valid paths to building your family.