Infertility, FemaleNATECNCT07450300
Assessment of the Feasibility of Frozen Embryo Transfers in a Natural Cycle Among Obese Compared to Non-Obese Patients
An observational study of Infertility, Female, run by Clinique Mathilde at 1 site in France.
Trial summary
This retrospective study included 1,831 single blastocyst frozen embryo transfer (FET) cycles performed between November 1, 2022 and August 31, 2025. Three endometrial preparation protocols were used according to ovulatory status, cycle duration, and characteristics of previous FET cycles: modified natural cycle with… Read more about this study
- Who is it for?
- Ages 18 to 45 years, women only
- Conditions the study is for
- Infertility, Female
- What is being tested?
- Modified natural cycle, Substitued cycle and Hormonal replacement therapy
- Type of treatment
- Pill or oral medicine, Surgery or procedure
- How many people
- 1,831 participants
- Where
- 1 siteFrance
- Study dates
- 1 Nov 2022to 31 Jan 2026
- Phase
- Observational
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 45 years
- Women only
- No healthy volunteers
- Adult
Study population: Women undergoing assisted reproductive technology (ART) with frozen embryo transfer (FET) at a tertiary fertility center were retrospectively identified. The study population included adult patients who underwent endometrial preparation using one of the following protocols: modified natural cycle with ovulation trigger, stimulated cycle, or hormone replacement therapy (HRT). Participants were categorized according to body mass index (BMI) into obese and non-obese groups for comparative analysis of embryo transfer feasibility and reproductive outcomes.
Women aged ≥18 years at the time of frozen embryo transfer.
Patients undergoing assisted reproductive technology (ART) with frozen embryo transfer (FET) using a natural, modified natural, stimulated, or hormone replacement therapy (HRT) protocol.
Availability of body mass index (BMI) measurement prior to initiation of the treatment cycle.
Trial locations and contacts
1 site in 1 country.
About this study
This retrospective study included 1,831 single blastocyst frozen embryo transfer (FET) cycles performed between November 1, 2022 and August 31, 2025. Three endometrial preparation protocols were used according to ovulatory status, cycle duration, and characteristics of previous FET cycles: modified natural cycle with ovulation trigger (mNC-FET) (n = 770), stimulated cycle FET (SC-FET) (n = 468), and hormone replacement therapy FET (HRT-FET) (n = 593). In natural cycles, if the predefined criteria for ovulation trigger were not met, the cycle was converted to a stimulated cycle. The aim of this study was to determine whether body mass index affects embryo transfer feasibility, reproductive outcomes, and cycle characteristics across different FET protocols.
- Conditions
- Infertility, Female
- Being tested
- Modified natural cycle, Substitued cycle, Hormonal replacement therapy
- Medical subject headings
- Infertility, Female
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Modified natural cycleProcedure or surgery
In the modified natural cycle group, patients underwent ultrasound and hormonal monitoring to track spontaneous follicular development. When the leading follicle reached an appropriate size and endometrial thickness was adequate, ovulation was triggered using human chorionic gonadotropin (hCG) to schedule frozen embryo transfer.
Substitued cycleProcedure or surgery
In the stimulated cycle group, mild ovarian stimulation was performed using oral agents and/or low-dose gonadotropins to promote follicular development. Follicular growth was monitored by ultrasound, and ovulation was either triggered with hCG or occurred spontaneously, allowing scheduling of frozen embryo transfer.
Hormonal replacement therapyProcedure or surgery
In the hormone replacement therapy group, endometrial preparation was achieved through exogenous estrogen administration. Once adequate endometrial thickness was confirmed, progesterone supplementation was initiated to mimic the luteal phase and schedule frozen embryo transfer.
| Study group | Role | What they receive |
|---|---|---|
| Modified natural cycle | Not described Receives: Procedure: Modified natural cycle | |
| Stimulated cycle | Not described Receives: Procedure: Substitued cycle | |
| Hormonal replacement therapy | Not described Receives: Procedure: Hormonal replacement therapy |
What is being measured
The primary outcome is the main question the study is designed to answer.
feasibility of embryo transfer
Proportion of treatment cycles in which the planned frozen embryo transfer (FET) was performed as scheduled, regardless of the number of embryos transferred.
Measured: scheduled day of embryo transfer (Day 0 of planned FET cycle)
Secondary outcomes (4)
Clinical pregnancy
Presence of an intrauterine gestational sac with fetal cardiac activity confirmed by transvaginal ultrasound.
Measured: 6 weeks after embryo transfer
Miscarriage rate
Pregnancy loss occurring after confirmation of clinical pregnancy and before 12 completed weeks of gestation.
Measured: 12 weeks of gestation
Cycle cancellation rate
Proportion of initiated FET cycles in which embryo transfer was not performed due to inadequate endometrial development, ovulation disorder, premature luteinization, or other clinical reasons.
Measured: scheduled day of embryo transfer
Conversion from natural to stimulated cycles
Proportion of cycles initially planned as natural or modified natural cycles that required initiation of ovarian stimulation due to insufficient follicular development or ovulatory dysfunction.
Measured: time of treatment protocol modification during the stimulation phase (prior to ovulation trigger)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted4 Mar 2026
- Study start1 Nov 2022
- Primary completion31 Aug 2025
- Study completion31 Jan 2026
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Infertility, FemaleStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Observational
- Observational model
- Cohort
- Time perspective
- Retrospective
- Enrolment
- 1,831 participants (actual)
Sponsor and investigators
- Lead sponsor
- Clinique Mathilde
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07450300
- Sponsor's protocol ID
- 2025-16-CMR
- Acronym
- NATEC
- Status last verified
- Mar 2026
- First submitted
- 19 Feb 2026
- Last updated
- 4 Mar 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 4 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Assessment of the Feasibility of Frozen Embryo Transfers in a Natural Cycle Among Obese Compared to Non-Obese Patients
- ClinicalTrials.gov ID
- NCT07450300
- Acronym / sponsor ID
- NATEC / 2025-16-CMR
- Conditions
- Infertility, Female
- Study type
- Observational
- Recruitment status
- Completed
- Enrolment
- 1,831 participants (actual)
- Lead sponsor
- Clinique MathildeUniversity, hospital or other
- Study start
- 1 Nov 2022 (actual)
- Primary completion
- 31 Aug 2025 (actual)
- Study completion
- 31 Jan 2026 (actual)
- First posted
- 4 Mar 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This retrospective study included 1,831 single blastocyst frozen embryo transfer (FET) cycles performed between November 1, 2022 and August 31, 2025. Three endometrial preparation protocols were used according to ovulatory status, cycle duration, and characteristics of previous FET cycles: modified natural cycle with ovulation trigger (mNC-FET) (n = 770), stimulated cycle FET (SC-FET) (n = 468), and hormone replacement therapy FET (HRT-FET) (n = 593). In natural cycles, if the predefined criteria for ovulation trigger were not met, the cycle was converted to a stimulated cycle. The aim of this study was to determine whether body mass index affects embryo transfer feasibility, reproductive outcomes, and cycle characteristics across different FET protocols.
Study design
- Observational model
- Cohort
- Time perspective
- Retrospective
- Number of arms
- 3
| Arm | Type | Receives |
|---|---|---|
| Modified natural cycle | – | Procedure: Modified natural cycle |
| Stimulated cycle | – | Procedure: Substitued cycle |
| Hormonal replacement therapy | – | Procedure: Hormonal replacement therapy |
Who may qualify
- Ages
- 18 to 45 years
- Sex
- Female only
- Healthy volunteers
- Not accepted
- Age groups
- Adult
- Study population
- Women undergoing assisted reproductive technology (ART) with frozen embryo transfer (FET) at a tertiary fertility center were retrospectively identified. The study population included adult patients who underwent endometrial preparation using one of the following protocols: modified natural cycle with ovulation trigger, stimulated cycle, or hormone replacement therapy (HRT). Participants were categorized according to body mass index (BMI) into obese and non-obese groups for comparative analysis of embryo transfer feasibility and reproductive outcomes.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Modified natural cycleIn the modified natural cycle group, patients underwent ultrasound and hormonal monitoring to track spontaneous follicular development. When the leading follicle reached an appropriate size and endometrial thickness was adequate, ovulation was triggered using human chorionic gonadotropin (hCG) to schedule frozen embryo transfer. | Procedure or surgery | Modified natural cycle |
| Substitued cycleIn the stimulated cycle group, mild ovarian stimulation was performed using oral agents and/or low-dose gonadotropins to promote follicular development. Follicular growth was monitored by ultrasound, and ovulation was either triggered with hCG or occurred spontaneously, allowing scheduling of frozen embryo transfer. | Procedure or surgery | Stimulated cycle |
| Hormonal replacement therapyIn the hormone replacement therapy group, endometrial preparation was achieved through exogenous estrogen administration. Once adequate endometrial thickness was confirmed, progesterone supplementation was initiated to mimic the luteal phase and schedule frozen embryo transfer. | Procedure or surgery | Hormonal replacement therapy |
Primary outcome
feasibility of embryo transfer
Time frame: scheduled day of embryo transfer (Day 0 of planned FET cycle)
Proportion of treatment cycles in which the planned frozen embryo transfer (FET) was performed as scheduled, regardless of the number of embryos transferred.
4 secondary outcomes
Clinical pregnancy
Time frame: 6 weeks after embryo transfer
Miscarriage rate
Time frame: 12 weeks of gestation
Cycle cancellation rate
Time frame: scheduled day of embryo transfer
Conversion from natural to stimulated cycles
Time frame: time of treatment protocol modification during the stimulation phase (prior to ovulation trigger)
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 4 Mar 2026.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
An observational study of Infertility, Female, run by Clinique Mathilde at 1 site in France.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 4 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in France. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
feasibility of embryo transfer (time frame: scheduled day of embryo transfer (Day 0 of planned FET cycle)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 4 Mar 2026.