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

NCT07450300 | Completed

• 1 other identifier: 2025-16-CMR
• Study Type: observational
• Target: 1,831
• Locations: 1 country
• Sites: 1

Brief 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 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

Outcome Measures

Primary Outcomes (1)

• 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.

  scheduled day of embryo transfer (Day 0 of planned FET cycle)

Secondary Outcomes (4)

• Clinical pregnancy

  6 weeks after embryo transfer

• Miscarriage rate

  12 weeks of gestation

• Cycle cancellation rate

  scheduled day of embryo transfer

• Conversion from natural to stimulated cycles

  time of treatment protocol modification during the stimulation phase (prior to ovulation trigger)

Study Arms (3)

Modified natural cycle

Procedure: Modified natural cycle

Stimulated cycle

Procedure: Substitued cycle

Hormonal replacement therapy

Procedure: Hormonal replacement therapy

Interventions

Modified natural cycle PROCEDURE

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.

Modified natural cycle

Substitued cycle PROCEDURE

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.

Stimulated cycle

Hormonal replacement therapy PROCEDURE

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.

Hormonal replacement therapy

Eligibility Criteria

• Age: 18 Years - 45 Years
• Sex: female
• Healthy Volunteers: No
• Age Groups: Adult (18-64)
• 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.

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.

Contact the study team to discuss eligibility requirements. They can help determine if this study is right for you.

Sponsors & Collaborators

• Clinique Mathilde: lead

Study Sites (1)

Clinique Mathilde

Rouen, 76000, France

Location

MeSH Terms

Conditions

Infertility, Female

Condition Hierarchy (Ancestors)

Genital Diseases, Female; Female Urogenital Diseases; Female Urogenital Diseases and Pregnancy Complications; Urogenital Diseases; Genital Diseases; Infertility

Study Design

• Study Type: observational
• Observational Model: COHORT
• Time Perspective: RETROSPECTIVE
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Study Record Dates

• First Submitted: February 19, 2026
• First Posted: March 4, 2026
• Study Start: November 1, 2022
• Primary Completion: August 31, 2025
• Study Completion: January 31, 2026
• Last Updated: March 4, 2026

Record last verified: 2026-03

Data Sharing

• IPD Sharing: Will not share

Locations

FR (1)