The rise in frozen embryo transfer (FET) cycles within assisted reproductive technology (ART) has sparked the need to refine endometrial preparation protocols. The switch from hormone replacement cycles (HRT) to natural cycles, poses scheduling challenges onto laboratories, doctors and patients. The modified natural cycle (mNC), offering more precision for scheduling, shows promise but lacks comprehensive data on the potential flexibility of triggering criteria that may allow to control timing in a wider range.
This prospective randomized study seeks to address this knowledge gap by evaluating the non-inferiority of triggering ovulation in mNC with follicle diameters of 13-16.9mm compared to the conventional 17-22mm.
The study aims to enhance the understanding of the impact of follicle size at ovulation in reproductive outcomes, optimize FET treatments providing a more flexible mNC protocol, and improve patient care in ART clinics.
At least one expanded blastocyst (regardless of its quality)
Spontaneous menstrual cycles
Consent to undergo frozen embryo transfer in a modified natural cycle
Abnormal uterine cavity
Fluid in endometrial cavity
Parallel
Trigger at smaller folicular size
Procedure/SurgeryTrigger indicated at folicular diameter smaller than standard clinical practice, from 13mm to 16.9mm
Pregnancy rate
Rate of positive pregnancies over total transfers performed, according to beta-test result
Implantation rate
Implantation rate, defined as number of gestational sacs per embryos transferred
Cancelation rate
Number of cancelled embryo transfers per initiated endometrial preparation cycles. Transfer canceling implies end of study.
Miscarriage rate
Number of miscarriages of any type registered after transfer during the study, per total number of transfers performed
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