Fresh or Frozen: What’s the Difference Between These Types of Embryo Transfers?
If you’re experiencing infertility and have decided to go down the road of ART (Assisted Reproductive Technology) and eventually the IVF process (in-vitro fertilization), you will be faced with a decision about the timing of your embryo transfer. Ideally, your doctor will monitor your body and give you the best information for your own personal cycle, helping to make the right decision for you (with your approval).
Fresh vs. frozen embryo transfer
When it comes to embryo transfers, there are two types, fresh or frozen—with the biggest difference being around timing.
A fresh embryo transfer is one that occurs soon after egg retrieval. This is when a healthy embryo is created in a lab outside of the woman’s body and then put back into the uterus—ideally around 3-5 days after the eggs were initially retrieved.
Similar to a fresh transfer, a frozen embryo transfer (FET) means the embryos are created in a lab outside a woman’s body, but this time the embryos are then frozen for use at a later date.
Let’s break down the main differences and discuss the benefits of each transfer type.
Reasons to choose a frozen transfer:
Preimplantation genetic testing
One of the benefits of using IVF for family building is the ability to select the embryo with the best chance of achieving a live birth. There are different tests embryos may undergo, and they each come with their own acronyms: PGD (preimplantation genetic diagnosis, which tests for specific disorders and chromosomal abnormalities), PGT-A (preimplantation genetic testing for aneuploidy)—and more.
By identifying the healthiest embryos before implantation, there is a higher likelihood of pregnancy, more single embryo transfers, and a lower probability of miscarriage. It can also reduce or eliminate more invasive genetic testing during pregnancy.
Ovarian hyperstimulation syndrome
Another significant reason to follow the FET path is OHSS: ovarian hyperstimulation syndrome. As the Mayo Clinic succinctly explains: “Ovarian hyperstimulation syndrome is an exaggerated response to excess hormones. It usually occurs in women taking injectable hormone medications to stimulate the development of eggs in the ovaries. Ovarian hyperstimulation syndrome causes the ovaries to swell and become painful.”
Let me break this one down: when we take all the meds to get all the eggs to make all the embryos, our ovaries can work triple time, and they need a reset and a rest. After loading up on the medications we need in order to stimulate follicle production and get an abundance of eggs, the ovaries can become engorged, causing the blood vessels to swell and leak fluid into areas of the abdomen. This results in pain and risk to varying degrees. Sometimes we simply need our body to regulate and balance our hormones.
In these modern times when monitoring is extensive, OHSS is rare. The Cleveland Clinic reports under 5% of women may experience OHSS.
Human chorionic gonadotropin (hCG), or the “pregnancy hormone,” can heighten the risk of OHSS. Given that hCG is often given to trigger the timed release of follicles for retrieval, we have to pay special attention to the body’s reaction. It’s important to note that a different type of trigger, known as gonadotropin-releasing hormone (GnRH) agonist trigger, may now be offered, which can help significantly reduce the risk of OHSS. We don’t want to add to the risk of poor body response to the hCG if pregnancy happens. Therefore, it makes sense to wait to transfer embryos until the ovaries have been given a chance to settle down after retrieval and the stimulating drugs. In such cases, freezing embryos (with or without testing) will be the best option for the parent-to-be. They can let their body heal, sometimes on its own and sometimes with medical help.
Synchrony for better cycles
As we’ve already talked about, there is so much more control that can happen with IVF for a process that typically feels completely out of control most of the time. We have even more control with frozen cycles in particular.
When we use frozen embryos, we have to create the perfect environment for them to implant within the uterus. Your doctor will give you the optimal amounts of estrogen and progesterone for your own body to ensure the uterine lining is growing to a desired thickness, which is ideal for implantation of the thawed embryo(s). Doing an FET allows us to control this growth and environment. We can sync the growth, schedule accordingly, and plan, plan, plan.
The primary reasons to use a fresh transfer:
The best of both worlds
In a dream world, you’d get both a fresh transfer opportunity and an opportunity to freeze an embryo during a given cycle. You’d get more than one embryo and have an immediate shot at a fresh transfer to see what happens, as well as the opportunity to freeze one or more additional embryos (with or without testing) down the road. It is always important to remember that risks of miscarriage are higher with untested embryos particularly in older patients (35+), which is what we’re talking about in a fresh transfer.
As mentioned above, when considering a fresh transfer, remember that your doctor might offer an alternate “trigger” option (like the GnRH agonist trigger as opposed to hCG) to reduce the risk of OHSS. They will also likely monitor your progesterone levels and endometrial development closely towards the end of the cycle.
Timing of the “blasts”
It is known with clarity that the best stage of development for an embryo transfer is once the embryo grows to blastocyst stage (generally called blasts). This is why it is usually day 5 of embryo development or a “day 5 blast” that gets transferred, because on average, viable embryos reach that stage of development on day 5, indicating that they are growing in a healthy way. Sometimes it’s day 6, and even day 7, when embryos reach the blastocyst stage.
Some women, for a host of reasons, don’t get embryos that develop into that golden blastocyst stage. The embryo arrests along the way, somewhere between days 1 and 7. There is a theory that placing the embryo inside the uterus earlier via fresh transfer on day 3 of development before blastocyst stage is achieved can provide a better environment for embryo development. Again, as in all things ART, it is not foolproof, but this is a variable worth trying if nothing else has worked.
As a fresh transfer is all within the same IVF cycle, it is often less expensive because there may be less medications involved and you are falling within the same monitoring appointments that you’d already be attending for your retrieval cycle. Also, embryo testing can significantly increase the cost of treatment. If there is no known reason to test (no specific chromosomal abnormalities or genetic markers to look for, the female partner is not of advanced maternal age), you may decide to opt out of testing altogether.
The bottom line
Where does all of this information leave us? Which type of transfer should you try? The bottom line is that there is not a one-size-fits-all approach when it comes to ART. This is why it is crucial to find a fertility clinic and specialist who will evaluate your specific needs and tailor a path accordingly. For some, a frozen transfer is better, and for some, fresh is the way to go.
Advancements are being made daily within the world of reproductive technology. And while that means nothing is a guarantee, it also means that there just may be something else to try. And that’s a great thing.