At the recently held Congress of the European Society for Human Reproduction and Embryology (ESHRE) at IVI we have presented a study that shows a new protocol for frozen embryo transfer (FET) that allows transfers to be planned with greater flexibility -almost 7 days- without affecting the success of the treatment.
From artificial or substituted cycles to natural cycles
The way to proceed with assisted reproduction treatments in clinics has varied, from substituted or artificial cycles to natural cycles when transferring frozen embryos. Until now, this last procedure raised doubts due to a possible complication when planning the transfer.
This study has had a sample size of 3,000 embryos and has been led by Dr. Carlos Alonso, a gynecologist at IVI Madrid: “embryo transfer can be scheduled if the endometrium is ready when the follicles measure between 13 and 20 millimeters, without altering in any way the clinical results of the process”. The study entitled “A new mNC protocol that allows a 7-day window for FET planning” has been presented these days at the 39th edition of the ESHRE.
Advances on the transfer in natural cycle
The natural cycle is a much more comfortable and physiological process, but until now it was thought to be very rigid and made it difficult to perform the transfer on the most convenient day for the patient. And, although there were studies on this point of treatment, the reality is that they had limitations and a small sample size, which made it difficult to reach conclusions on which to advance.
“Our study, in a pioneering way, and with the largest sample size to date for a study of these characteristics, shows that the natural cycle is more physiological -since it hardly involves medication-, more comfortable, effective and safe, reducing gestational risks such as preeclampsia at the end of pregnancy. Analysis of these cases has allowed us to demonstrate how the endometrium acquires the necessary characteristics to ensure excellent implantation rates several days earlier than initially thought. Thus, these findings make it possible to provide the modified natural cycle with a flexibility of almost 7 days that was previously unknown, something very beneficial, since it favors that the moment of the transfer can be adapted to the personal or work needs of the patients. On the other hand, this flexibility is also positive for assisted reproduction clinics, since it allows the organization and equitable planning of the procedures”explains Dr. Alonso.
How is the transfer carried out in the natural cycle?
In the process of the modified natural cycle, the spontaneous development of the endometrium and the dominant follicle is controlled by ultrasound, until the moment of administering recombinant hCG as medication. This favors changes in said follicle, in addition to the transformation in the endometrium necessary for the transfer of an embryo to be carried out seven days later. Until now, the belief existed that the administration of recombinant hCG should be limited to the time when the dominant follicle reaches a diameter of 17 millimeters, measured by ultrasound. This was the main disadvantage compared to the currently most widely used endometrial preparation strategy: the estradiol-replaced hormone therapy cycle.
“Our study ends the rigidity of the modified natural cycle and allows its implementation to be easier in routine clinical practice, thus reducing medication costs, side effects, and obstetric complications associated with HRT”adds Dr. Alonso.
Advantages of embryo transfer in natural cycle
First, by adopting this protocol, the use of synthetic estrogens is completely avoided and the need for exogenous progesterone is halved. In addition, the discomfort of administering medication vaginally is minimized. On the other hand, the process implies a lower economic and emotional cost, as well as being less complex. This is because the costs of medication and monitoring are reduced, and visits to the clinic are reduced, which means greater well-being for patients. Finally, this process is physiologically more natural, since it is more similar to the natural process of the female body. Therefore, the process becomes easier and more bearable until the patient reaches pregnancy, also reducing the complications of the end of pregnancy, such as hypertensive disorders.
