Frozen Embryo Transfer (FET) is a widely used technique in assisted reproductive technology where frozen embryos from previous IVF cycles are thawed and transferred to the uterus. Successfully synchronizing the embryo transfer with the uterine lining readiness is critical, and that’s why different FET protocols are used. These protocols can be broadly categorized into three types: Natural cycle FET, Artificial cycle FET (also called Hormone Replacement Therapy or HRT cycle), and Stimulated cycle FET. Understanding each protocol helps patients and clinicians choose the best approach for individual needs.
Natural Cycle FET
In the natural cycle FET, no external hormones are used to prepare the uterine lining. Instead, the woman’s natural menstrual cycle is closely monitored to detect the precise time of ovulation. The embryo transfer is timed to match this natural ovulation window, allowing the embryo to be transferred into an optimally receptive uterus.
This option is particularly suitable for women who have regular ovulatory cycles and do not require additional hormonal support. It is considered the most physiological approach, with fewer medications and side effects. However, the timing has to be very precise, and it can be less convenient due to the need for frequent monitoring.
Artificial Cycle FET (HRT Cycle)
The artificial or HRT cycle FET is commonly used for women who have irregular menstrual cycles or ovulatory problems. In this protocol, exogenous estrogen and progesterone are administered to simulate the natural cycle and build up the endometrial lining to prepare the uterus for embryo implantation.
The advantage of this approach is that it offers greater control over timing since the cycle is driven entirely by medication. This makes scheduling more predictable for both patients and clinics. However, this involves taking hormonal medications which may cause side effects like mood swings or bloating.
Stimulated Cycle FET
Stimulated cycle FET combines elements of the natural and artificial protocols. It involves administering mild ovulation-inducing medications such as letrozole or clomiphene citrate to stimulate follicle development and ovulation in cases where women do not ovulate regularly.
This method supports better endometrial development and offers more flexibility in timing compared to the natural cycle, while using fewer hormones than the fully artificial approach. It’s suitable for women with mild ovulatory disturbances or irregular cycles.
Conclusion
Choosing the right FET protocol is a personalized decision based on menstrual regularity, medical history, and convenience. Each protocol — natural, artificial, or stimulated — offers unique benefits and challenges, but all have proven effectiveness in achieving pregnancy. Collaborating with a fertility specialist ensures the best protocol is selected to maximize the chances of a successful and healthy embryo transfer.