FET-LET-2x2: Testing natural vs medicated natural cycles for frozen embryo transfer
Official title: FET-LET-2x2: A Randomized Open-Label 2×2 Factorial Trial Comparing Clinical Pregnancy Rates After Frozen Embryo Transfer in True and Modified Natural Cycles With and Without Aromatase Inhibitors
Run by University of Novi Sad · NCT07425990 · Data updated 2026-11-12
This study tests four approaches to preparing the uterus for frozen embryo transfer to see which yields the best pregnancy rate in women undergoing IVF.
Quick facts
| Study type | Interventional |
|---|---|
| Ages | 18 Years to 40 Years |
| Sex | Women only |
| Enrollment | 120 (estimated) |
| Sponsor | University of Novi Sad Academic / other |
| Locations | 1 site (Novi Sad) |
| Status | Recruiting |
| Started | March 13, 2026 |
| Main results expected | February 2027 |
| Study ends | March 2027 |
| Registry record updated | September 29, 2026 |
| Trial ID | NCT07425990 on ClinicalTrials.gov |
Is this trial a fit for you?
✓Likely a good fit
Women aged 18-40 with regular cycles scheduled for FET in a natural cycle, and no significant uterine abnormalities.
✕Probably not a fit
Women with irregular cycles, significant uterine abnormalities, donor oocytes, or embryos with poor thaw survival may not benefit.
A plain-English reading of the study's rules. Only the study team can confirm whether you qualify.
What this trial studies
This interventional trial compares four natural-cycle protocols for uterine preparation before frozen embryo transfer. Participants are randomly assigned and monitored with ultrasound and hormone tests, with some groups receiving letrozole early in the cycle and others receiving hormonal support such as r-hCG or progesterone. The goal is to determine whether a completely natural cycle or a medicated natural cycle, and the use of letrozole, can improve clinical pregnancy rates. Outcomes are measured by ultrasound-confirmed pregnancy after the transfer.
Why it matters
Potential benefit: If successful, the findings could guide more effective, individualized FET preparation strategies to improve pregnancy chances.
How similar studies have gone: Previous research has explored natural versus medicated cycles, with mixed results; this study adds a randomized comparison across four approaches.
Who can join: the full rules
Show full inclusion / exclusion criteria
Inclusion Criteria: * Women aged 18 to 40 years * Regular menstrual cycles (26-35 days) * Scheduled for frozen embryo transfer (FET) in a natural menstrual cycle * Normal gynecological ultrasound findings without clinically significant uterine abnormalities * Ability to provide written informed consent Exclusion Criteria: * Use of preimplantation genetic testing (PGT) for the transferred embryo * Use of donor oocytes * Inadequate embryo survival after thawing, defined as loss of viability in more than 50% of blastomeres * Irregular menstrual cycles * Presence of clinically significant uterine abnormalities detected by ultrasound * Inability or unwillingness to provide written informed consent
Where it's running
-
Specialized Gynecological Hospital "Ferona" Novi Sad
Novi Sad, Serbia Recruiting
Study contacts
- Study coordinator: Jelena Vukovic, MD
- Email: jel.zor@gmail.com
- Phone: +381643070647
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How to take part
- Review the eligibility criteria above with your treating physician.
- Check the official listing on ClinicalTrials.gov for the latest contact details and recruitment status.
- Contact the study coordinator or principal investigator to ask for pre-screening. Pre-screening is free and never obligates you to enroll.