Types of frozen embryo transfers
Frozen embryo transfers can be done using different protocols: natural cycle FET, medicated FET, or modified natural FET. Let’s learn more about them.
Natural cycle frozen embryo transfer
A natural cycle frozen embryo transfer (FET) aligns the timing of the embryo transfer with your natural menstrual cycle. Unlike medicated cycles, it does not use additional hormones. Instead, it relies on your body’s natural production of oestrogen and progesterone to prepare the uterus for implantation.
How it works
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- Monitoring ovulation
The process starts with tracking your menstrual cycle to pinpoint ovulation. This is done using blood tests to check hormone levels and ultrasounds to monitor the growth of ovarian follicles.
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- Timing the transfer
After ovulation is detected, the embryo transfer is scheduled to match the natural rise in progesterone. This ensures your uterine lining is ready to support implantation.
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- Embryo transfer
A few days after ovulation, the embryo is thawed and transferred into the uterus, following your body’s natural rhythm.
Pros of Natural Cycle FET
Less medication: A natural cycle FET uses your body’s natural hormonal changes, so you need fewer medications. This means fewer injections and less stress, making the process simpler and more comfortable. With fewer drugs, there’s also a lower risk of side effects from hormonal treatments.
Natural environment: Using your natural cycle may create a better environment for implantation. Studies suggest that natural hormones can improve the chances of a successful pregnancy. When the body prepares the uterine lining naturally, it often responds better than with artificial hormone treatments.
Corpus luteum support: After ovulation, the corpus luteum in your ovary produces natural progesterone. This helps keep the uterine lining healthy, giving more support for implantation and early pregnancy.
Cons of Natural Cycle FET
Requires regular cycles: A natural cycle FET works best if you have regular menstrual cycles. Irregular cycles can make it harder to predict ovulation, which is essential for timing the embryo transfer.
More monitoring: You’ll need regular monitoring to pinpoint ovulation, including blood tests and ultrasounds. This might mean more visits to the clinic, which can feel inconvenient for some.
Less control: The timing of a natural cycle transfer is less predictable than a medicated cycle. This can make scheduling trickier for both you and the clinic.
Medicated (Artificial) frozen embryo transfer
A medicated FET uses hormones to prepare the uterus for embryo transfer, without relying on your natural menstrual cycle. Medications create the ideal conditions for implantation, ensuring the uterine lining is ready for the embryo.
How it works
Oestrogen supplements
You’ll start with oestrogen, taken as pills, patches, or injections. Oestrogen helps build a thick uterine lining (endometrium) to support implantation.
Progesterone supplements
Once the lining is ready, progesterone is added to stabilise it and make it receptive to the embryo. Progesterone can be taken as injections, vaginal suppositories, or oral medications.
Timing and monitoring
The timing of oestrogen and progesterone is carefully controlled and monitored. When your lining is ready, the embryo transfer is scheduled to give the best chance for success.
Pros of artificial FET
Greater control: One of the main advantages of a medicated FET is the ability to precisely control the timing of the embryo transfer. By using supplemental hormones, doctors can schedule the transfer at the most convenient time for the patient, ensuring the uterine lining is perfectly prepared for implantation. This control can lead to higher chances of success.
Flexibility: Medicated FET is suitable for women with irregular menstrual cycles or those who have had issues with the thickness or quality of their uterine lining in the past. Since the process does not rely on natural ovulation, it can accommodate a wider range of patients, including those who do not ovulate regularly or at all.
Consistency: Using medications ensures a consistent and reliable preparation of the endometrium, which can lead to better outcomes, especially for women who have had difficulties with natural cycle FETs.
Cons of artificial FET
More medications: Medicated FET requires taking several medications, which can have side effects such as bloating, mood swings, and fatigue. The increased use of drugs also makes the process more complex and may be daunting for some patients.
Increased monitoring: The need for regular monitoring through blood tests and ultrasounds to check hormone levels and the condition of the uterine lining can be time-consuming and may require frequent clinic visits.
Cost: The use of additional medications and increased monitoring can raise the overall cost of the treatment, which may be a consideration for some patients.
Modified natural frozen embryo transfer
A modified natural frozen embryo transfer (FET) combines aspects of natural and medicated cycles. It may include medication to trigger ovulation while relying on your body’s natural hormones to prepare the uterine lining. This approach aims to balance minimal medication with the precise timing of a medicated cycle.
How it works
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- Ovulation induction
Medication like letrozole or clomiphene is used to stimulate ovulation, ensuring it happens at a predictable time. This is key for scheduling the embryo transfer.
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- Monitoring
After ovulation is induced, your natural hormone levels (oestrogen and progesterone) are monitored with blood tests and ultrasounds. This helps determine the best time for the transfer.
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- Timing the transfer
When ovulation is confirmed and your uterine lining is ready, the embryo transfer is scheduled to align with your body’s natural cycle. This ensures the uterus is prepared for implantation with minimal reliance on additional medication.
Pros of Modified Natural FET
Balanced approach
A modified natural FET provides more control over the timing of the embryo transfer than a fully natural cycle while using less medication than a fully medicated cycle. It balances natural hormonal processes with the precision of medical intervention.
Flexibility and control
This method is ideal for women who ovulate naturally but need some assistance to optimise the timing of the transfer. It can be especially helpful for women with slightly irregular cycles or those needing support with ovulation.
Cons of Modified Natural FET
Moderate medication use
Although a modified natural FET uses less medication than a fully medicated cycle, it involves more than a purely natural cycle. This can cause some side effects, though they are usually mild compared to fully medicated cycles.
Increased monitoring
Close monitoring of hormone levels means more visits for blood tests and ultrasounds. This can be time-consuming and inconvenient for some people.