Assessment of the Feasibility of Frozen Embryo Transfers in a Natural Cycle Among Obese Compared to Non-Obese Patients (NATEC)

March 2, 2026 updated by: Clinique Mathilde
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 Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Completed

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Observational

Enrollment (Actual)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
1831

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • France
      • Rouen, France, 76000
        • Clinique Mathilde

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

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.

Description

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.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort

Group / Cohort

A group or subgroup of participants in an observational study that is assessed for biomedical or health outcomes.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Modified natural cycle
Procedure: Modified natural cycle
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.
Stimulated cycle
Procedure: Substitued cycle
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 therapy
Procedure: Hormonal replacement therapy
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.

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
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.
scheduled day of embryo transfer (Day 0 of planned FET cycle)

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
Clinical pregnancy
Time Frame: 6 weeks after embryo transfer
Presence of an intrauterine gestational sac with fetal cardiac activity confirmed by transvaginal ultrasound.
6 weeks after embryo transfer
Miscarriage rate
Time Frame: 12 weeks of gestation
Pregnancy loss occurring after confirmation of clinical pregnancy and before 12 completed weeks of gestation.
12 weeks of gestation
Cycle cancellation rate
Time Frame: scheduled day of embryo transfer
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.
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)
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.
time of treatment protocol modification during the stimulation phase (prior to ovulation trigger)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
Clinique Mathilde

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
November 1, 2022

Primary Completion (Actual)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
August 31, 2025

Study Completion (Actual)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
January 31, 2026

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
February 19, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 2, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
March 4, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
March 4, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
March 2, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
March 1, 2026

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 2025-16-CMR

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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