Course /Transferring Fresh or Frozen Embryos
What is a Fresh Embryo Transfer?
A fresh embryo transfer occurs within a single, continuous cycle. The surrogate’s menstrual cycle is synchronized with the egg retrieval of the intended mother or egg donor. After retrieval, the eggs are fertilized, and the resulting embryos are cultured for 3-5 days. Without being frozen, the most viable embryo is selected and transferred into the surrogate’s uterus during her implantation window.
Key Characteristic:Â The transfer happens in the same cycle as the stimulation and retrieval.
The Synchronization Challenge:Â This protocol requires precise timing to align the development of the embryos with the readiness of the surrogate’s uterine lining.
What is a Frozen Embryo Transfer (FET)?
A frozen embryo transfer, often called a “freeze-all” cycle, decouples the egg retrieval process from the transfer process. All viable embryos created from the retrieval are cryopreserved (frozen) using a rapid-freezing technique called vitrification. The transfer occurs in a subsequent, separate cycle. The surrogate’s uterine lining is prepared with estrogen and progesterone, allowing for optimal control over the implantation environment.
Key Characteristic:Â The egg retrieval/fertilization and embryo transfer are two distinct events, separated by at least one month.
The Flexibility Advantage:Â This approach allows the clinical team to optimize the surrogate’s uterine environment independently of the hormone fluctuations caused by ovarian stimulation.
The success of embryo implantation hinges on a perfect synchrony between a developing embryo and a receptive uterine lining. This short period, known as the “window of implantation,” is a critical concept in understanding the shift towards frozen transfers.
The Impact of Ovarian Stimulation on the Endometrium
During a fresh cycle, the intended mother or egg donor undergoes ovarian stimulation with hormones (gonadotropins) to produce multiple eggs. This creates a supraphysiological hormonal environment, with elevated estrogen and progesterone levels. Research indicates that these high hormone levels can:
Advance the Endometrial Window:Â Cause the uterine lining to mature too quickly, closing the window of implantation earlier than expected.
Alter Gene Expression:Â Affect the molecular dialogue between the embryo and the endometrium, potentially making it less receptive.
Cause Asynchrony:Â Create a mismatch where a perfectly good embryo is transferred into a uterus that is not at its optimal state of receptivity.
The Controlled Environment of a Frozen Transfer
In a frozen embryo transfer cycle, the surrogate’s uterus is prepared in a more controlled, naturalistic hormonal environment. Since there is no ovarian stimulation involved for the surrogate, her lining is built with exogenous hormones, allowing clinicians to precisely tailor the timing of progesterone exposure to open the window of implantation. This control often leads to a more favorable and predictable endometrial environment, potentially increasing the chances of a successful implantation.
The rise of vitrification, which has vastly improved embryo survival rates post-thaw, has led to a wealth of data comparing the two approaches. In several key scenarios, a “freeze-all” strategy demonstrates clear benefits.
1. Risk of Ovarian Hyperstimulation Syndrome (OHSS)
This is the most critical medical indication for freezing all embryos. If the intended mother or egg donor is at high risk for OHSS, a fresh transfer can significantly worsen the condition because a resulting pregnancy produces its own hCG, exacerbating the syndrome. Electively freezing all embryos and delaying transfer allows the stimulated cycle to resolve completely, protecting the health of the egg provider.
2. Preimplantation Genetic Testing (PGT)
For Intended Parents utilizing PGT to screen embryos for chromosomal abnormalities (aneuploidy), a frozen transfer is mandatory. The biopsy process and the time required for the genetic lab to return results (usually 1-2 weeks) make a fresh transfer logistically impossible. This ensures that only genetically normal embryos are selected for transfer.
3. Suboptimal Endometrial Preparation
If monitoring during stimulation reveals that the surrogate’s uterine lining is too thin, has an irregular pattern, or shows premature progesterone rise, proceeding with a fresh transfer is not advisable. Freezing the embryos allows the medical team to stop the cycle, let the surrogate’s body reset, and prepare her lining more effectively in a future FET cycle.
4. High Responders and Peak Estrogen Levels
As mentioned in the context of the “window of receptivity,” patients who are high responders with very high estrogen levels during stimulation may have a compromised endometrial environment. Studies have shown that in these cases, frozen transfers can lead to higher live birth rates compared to fresh transfers.
Despite the strong trends towards freezing, a fresh embryo transfer remains a viable and sometimes preferred option in certain contexts.
1. Simplicity and Efficiency
A fresh transfer is a single, continuous process. For some Intended Parents, the appeal of a “one-and-done” cycle—from retrieval to transfer without interruption—is significant. It can reduce the overall timeline to transfer and may feel like a more straightforward journey.
2. Cost Considerations (in specific scenarios)
While the overall success rates may favor FET in many cases, a fresh transfer avoids the costs associated with embryo freezing, storage, and the subsequent frozen embryo transfer cycle medications and monitoring. In a scenario with a perfect clinical picture (excellent embryo quality, ideal endometrial lining, and no risk factors), a fresh transfer can be a cost-effective first attempt.
3. Specific Patient Populations & Clinic Protocols
Some studies suggest that for certain patient groups, such as those with a low prognosis or younger patients, the success rates between fresh and frozen transfers may be comparable. Furthermore, some clinics, based on their specific culture medium and laboratory protocols, have historically achieved excellent results with fresh transfers and may recommend them based on their own internal data.
Conclusion: A Personalized Clinical Decision
The choice between a fresh and frozen embryo transfer is not one-size-fits-all. It is a nuanced decision that your fertility specialist will make based on a multitude of factors, including the egg provider’s response to stimulation, the surrogate’s endometrial development, embryo quality, and whether genetic testing is being utilized.
At Surrogacy4All, we work closely with top-tier IVF clinics that leverage the latest data and technologies. Our role is to ensure you understand these complex medical decisions, so you can partner confidently with your clinical team to choose the path that offers the highest chance of a healthy, successful pregnancy for your surrogate.
Our job is to listen, to connect the dots between your needs, and to determine how we can best help you have your baby. If you’re asking how much does it cost for a surrogate, we’ll walk you through every step of the process to ensure there are no surprises.
To make an appointment with one of our counselors or physicians, please call (212) 661-7673 or email info@surrogacy4all.com. We look forward to hearing from you.
Surrogacy4All is a unique international surrogacy service targeted at providing state of the art IVF and surrogacy services to Intended Parents irrespective of age, sex or color, at the lowest possible cost in the world.
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