Triggering Ovulation at Follicle Size Smaller or Larger Than 17mm in a Modified Natural Cycle

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.

NCT Number	NCT07088952
Lead Sponsor	Vida Recoletas Sevilla
Conditions	Embryo Transfer
Enrollment	572 participants
Start Date	2025-10-22
Primary Completion	2027-07-30 (estimated)
Study Completion	2028-05-30 (estimated)
Updated on ClinicalTrials.gov	2026-01-13