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Clinical trial Recruiting at 1 site Interventional Ages 18 to 50 Women only

Triggering ovulation at smaller versus larger follicle sizes in a modified natural cycle

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

Run by Vida Recoletas Sevilla · NCT07088952 · Data updated 2026-11-12

This trial tests whether triggering ovulation when follicles are 13–16.9 mm works as well as triggering at 17–22 mm for people having a modified natural cycle frozen embryo transfer.

Quick facts

Study typeInterventional
Ages18 Years to 50 Years
SexWomen only
Enrollment572 (estimated)
SponsorVida Recoletas Sevilla
Academic / other
Locations1 site (Seville, Sevilla)
StatusRecruiting
StartedOctober 22, 2025
Main results expectedJuly 30, 2027
Study endsMay 30, 2028
Registry record updatedJanuary 13, 2026
Trial IDNCT07088952 on ClinicalTrials.gov

Is this trial a fit for you?

Likely a good fit

Ideal candidates are people with regular spontaneous cycles planning an mNC frozen embryo transfer who have at least one expanded blastocyst and no uterine cavity abnormalities.

Probably not a fit

People with abnormal uterine cavities, endometrial fluid, irregular or suppressed cycles, or those requiring hormone replacement endometrial preparation are unlikely to benefit from this protocol.

A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.

What this trial studies

This is a prospective randomized non-inferiority trial comparing ovulation triggers at follicle diameters of 13–16.9 mm versus the conventional 17–22 mm in a modified natural cycle (mNC) frozen embryo transfer (FET) setting. Eligible participants have spontaneous menstrual cycles, at least one expanded blastocyst, and consent to mNC FET, while those with abnormal uterine cavity or intrauterine fluid are excluded. Participants are randomized to early or standard follicle-size trigger groups and followed for implantation and pregnancy outcomes to compare reproductive success. The study seeks to determine if earlier triggering preserves pregnancy rates while increasing scheduling flexibility for clinics and patients.

Why it matters

Potential benefit: If successful, this approach could allow clinics and patients to schedule FETs more flexibly without reducing pregnancy success.

How similar studies have gone: Some smaller studies and clinic reports suggest flexibility in mNC timing may be safe, but randomized non-inferiority data specifically comparing 13–16.9 mm versus 17–22 mm triggers are limited.

Who can join: the full rules

Show full inclusion / exclusion criteria 
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

Where it's running

  • Vida Recoletas Sevilla
    Seville, Sevilla, Spain     Recruiting

Study contacts

Similar studies

Other studies for the same condition or treatment. Recruiting studies are listed first.

How to take part

  1. Review the eligibility criteria above with your treating physician.
  2. Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
  3. Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.
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Last reviewed 2026-11-14 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.