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Key takeawaysEmbryo transfer protocolsFAQsReferences

Key takeaways

  • Frozen embryo transfer (FET) requires the uterus to be carefully prepared, and clinics currently use several different hormonal protocols to do this.
  • The most natural approach involves close monitoring across the cycle to pinpoint ovulation precisely, which means frequent clinic visits and blood tests.
  • A new pilot study, co-authored by Genea Melbourne's Medical Director, Associate Professor Alex Polyakov, is testing a modified protocol that uses a progesterone pessary to prepare the uterine lining, without needing to pinpoint the exact moment of ovulation.
  • This is a feasibility study, its purpose is to test whether the modified protocol can work well in practice, ahead of any conclusions about pregnancy outcomes.
  • If successful, this kind of approach could offer patients greater flexibility and fewer appointments during FET preparation.

What is frozen embryo transfer, and why does the protocol matter?

Frozen embryo transfer (FET) involves thawing a previously frozen embryo and transferring it into the uterus, often in a cycle separate from the original egg collection. Before this can happen, the uterine lining needs to be carefully prepared so it is ready to support an embryo at exactly the right time, a window known as the window of implantation.

There is more than one way to achieve this. Clinics currently use a range of protocols, including the true natural cycle, modified natural cycle, artificial cycle, and ovulation induction approaches. Each has its own advantages and trade offs, particularly around how precisely ovulation needs to be timed and how flexible the process can be for patients.

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The challenge with current FET protocols

The most natural approach to FET preparation relies on tracking a patient's own hormonal cycle closely, using regular blood tests and ultrasounds to pinpoint the precise moment of ovulation. While this avoids some of the additional hormone medications used in other protocols, it asks a lot of patients in terms of time and clinic visits, and requires careful, ongoing monitoring to get the timing right.

More recently, a different approach has emerged, one where the need to closely monitor or trigger ovulation is reduced. Instead, luteal phase support, using a progesterone pessary, begins once certain follicle size and uterine lining thickness criteria are met, but before ovulation actually occurs. This could mean less reliance on catching ovulation at the exact right moment. However, the existing research into this approach has some important limitations, which is what this new study seeks to address.

What this new study is testing

This pilot cohort study, published as a study protocol in JMIR Research Protocols, is designed to test the feasibility of this progesterone modified natural cycle protocol for FET. The research team includes Genea Melbourne's Medical Director, Associate Professor Alex Polyakov, alongside colleagues Alexandra Churchill, Ektoras Georgiou, Veronica Abruzzo and Wan Tinn Teh.

It is important to understand what this study is, and is not. This is a protocol paper, meaning it sets out the design of a pilot study rather than reporting final pregnancy or live birth outcomes. Its primary aim is to assess whether this modified approach is practically feasible, before larger studies go on to test its effectiveness in more detail.

What researchers hope to learn

The modified protocol being tested removes the need to pinpoint the exact moment of ovulation. Instead, a progesterone pessary is used to support the uterine lining once specific follicle size and endometrial thickness criteria are met. If feasible, this approach could reduce the number of monitoring appointments patients need during FET preparation, without compromising how well the uterine lining is prepared for transfer.

Because this is a pilot feasibility study, its early results are expected to help determine whether this simplified protocol works well enough in practice to justify further research into pregnancy outcomes at a larger scale. It is a first, important step, not a final answer.

At Genea, we are proud to have researchers like Associate Professor Alex Polyakov contributing to studies like this one, work that reflects our broader commitment to finding ways to make fertility treatment more manageable for patients, without ever compromising on quality of care.

What this means for you

If you are preparing for a frozen embryo transfer, it is worth knowing that researchers are actively exploring ways to make the preparation process simpler and more flexible for patients. This particular study has not yet produced final outcome data, so it does not change current FET protocols used in clinic today.

Your fertility specialist will recommend the FET protocol best suited to your individual cycle, medical history and preferences. If you are curious about how different protocols compare, or whether newer approaches like this one may become relevant to your care in future, this is a great conversation to have with your care team.

FAQs

About the authors

Alex Polyakov

Dr. Alex Polyakov

Medical Director Melbourne City and Fertility Specialist MBBS, MClinEpid, MReproMed, MHlth&MedLaw, MBioeth, GradCertEBM, FACLM, FANZCOG

Melbourne Fertility Specialist A/Prof Alex Polyakov at Genea. Complete fertility care from IVF to delivery, combining clinical expertise & academic research.

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References

  1. Churchill, A., Georgiou, E., Abruzzo, V., Polyakov, A., & Teh, W. T. (2025). Feasibility of a progesterone-modified natural protocol for frozen embryo transfer: Protocol for a pilot cohort study. JMIR Research Protocols, 14, e66579. https://doi.org/10.2196/66579
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