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NCT Number: NCT07088952

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.

Recruiting

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Key information

Conditions

Embryo Transfer

Age range

18 year–50 year

Sex eligibility

Female

Study type

Interventional

Phase

Not applicable

Primary location

Vida Recoletas Sevilla

Seville, Sevilla, 41092, Spain

Location status: Recruiting

Location contact

Clara Palacio de Marco, MSc

CONTACT

[email protected]

+34954286274

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • At least one expanded blastocyst (regardless of its quality)
  • Spontaneous menstrual cycles
  • Consent to undergo frozen embryo transfer in a modified natural cycle

Exclusion criteria

  • Abnormal uterine cavity
  • Fluid in endometrial cavity

Treatment and study plan

Trigger at smaller folicular size

Procedure

Trigger indicated at folicular diameter smaller than standard clinical practice, from 13mm to 16.9mm

Primary outcomes

  1. Pregnancy rate

    Time frame: From embryo transfer up to 2 weeks later

    Rate of positive pregnancies over total transfers performed, according to beta-test result

Secondary outcomes

  1. Implantation rate

    Time frame: up to 8 weeks of gestational age

    Implantation rate, defined as number of gestational sacs per embryos transferred

  2. Cancelation rate

    Time frame: Perioperative/Periprocedural

    Number of cancelled embryo transfers per initiated endometrial preparation cycles. Transfer canceling implies end of study.

  3. Miscarriage rate

    Time frame: From embryo transfer to delivery, up to 40 weeks

    Number of miscarriages of any type registered after transfer during the study, per total number of transfers performed

Study contacts

Contact information is provided by the study sponsor or research team.

Clara Palacio de Marco, MSc

CONTACT

[email protected]

+34954286274

Manuel Fernández Sánchez, MD PhD

CONTACT

[email protected]

+34954286274

Sponsors and collaborators

Lead sponsor

Vida Recoletas Sevilla

Other

Registry information

Acronym: 17FET

Important dates

Study start
2025
Primary completion
2027
Study completion
2028
First posted
Jul 28, 2025
Registry last updated
Jan 13, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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