06/11/2025
Modified natural FET (mNFET) protocol :
It is an assisted reproductive technology method for frozen-thawed embryo transfer that uses the woman's natural menstrual cycle but also includes medical intervention to trigger ovulation and support the uterine lining. Unlike a true natural cycle, an mNFET involves administering an injection, typically hCG, once a dominant follicle reaches a certain size, which gives more flexibility in scheduling the transfer while still utilizing the body's own hormones for ovulation and endometrial development. This can be an alternative to medicated FET for those who prefer to minimize medication and have regular cycles.
Key features of the mNFET protocol
Natural cycle monitoring: The protocol starts by monitoring the woman's natural cycle with ultrasounds and blood tests to track the growth of a dominant follicle and the thickening of the uterine lining.
Hormonal support: The body produces its own estrogen and progesterone, but the protocol typically includes some supplemental progesterone, often a vaginal suppository, to help prepare the uterine lining.
Ovulation trigger: Unlike a true natural cycle where ovulation is triggered by the body's own LH surge, an mNFET uses an injection of human chorionic gonadotropin (hCG) to trigger ovulation when the follicle is mature. This provides flexibility in scheduling the transfer.
Embryo transfer timing: The embryo transfer is scheduled a specific number of days after the hCG trigger (e.g., six days) or based on progesterone levels, making it easier to plan than a true natural cycle.
Potential modifications: Some protocols may include other medications, such as letrozole at the start of the cycle, to help with follicle development. In some cases, an antagonist might be used to prevent a premature spontaneous ovulation, particularly for weekend transfers.
Benefits of mNFET
Flexibility: The hCG trigger allows for a more flexible transfer schedule compared to a true natural cycle, which can be difficult to schedule precisely.
Reduced medication: It requires less medication compared to a fully medicated FET, avoiding the need for high-dose, long-term intramuscular progesterone injections.
Potential to benefit specific patients: Some studies have found that natural cycle FETs may have benefits for patients with a history of repeated implantation failure.
Who is it for?
This protocol is often suitable for women who have regular menstrual cycles and can reliably produce a dominant follicle and a lining of sufficient thickness.
