Natural Frozen Embryo Transfer (FET) vs Substituted Frozen Embryo Transfer (FET)

December 3, 2025 updated by: Clinique Ovo

Embryo Transfer in Natural vs Substituted Cycle and the Scheduling Pattern of IVF

In frozen embryo transfer substituted cycles, patients are treated with progesterone and estrogen in an attempt to mimic the natural cycle and a transfer is planned whenever the endometrium is ready. In contrast, in frozen embryo transfer natural cycle patients are not taking any hormones, only triggered with hCG (human chorionic gonadotropin) when a dominant follicle is ready or they wait for the disappearance of the dominant follicle to plan the transfer date. Some doctors and centres shift towards using the substituted protocol in an attempt to make scheduling easier with less frequent ultrasounds.

This study will aim to compare clinical and biochemical pregnancy rates in patients who underwent frozen embryo transfers in natural cycles vs substituted cycles at the centre.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Study Type

Observational

Enrollment (Actual)

1207

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

  • Canada
    • Quebec
      • Montreal, Quebec, Canada, H4P 2S4
        • Clinique ovo

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

Ages Eligible for Study

  • Child
  • Adult

Accepts Healthy Volunteers

N/A

Sampling Method

Probability Sample

Study Population

Data spreadsheet from Jan 2022 to March 2023 of patients undergoing natural or substituted frozen embryo transfer

Description

Inclusion Criteria:

  • Age < 40 years old
  • Women having undergone either a frozen embryo transfer in natural cycle or substituted cycle
  • IVF and FET cycles done at Clinique OVO

Exclusion Criteria:

  • egg or embryo recipient
  • History of recurrent miscarriages, defined as ≥ 3 consecutive losses
  • Patients that needed Viagra, Plasma-Rich Platelet (PRP) or other modalities to improve their endometrial thickness
  • Uterine abnormalities
  • Abnormal hormonal profiles
  • FET Stimulated cycles
  • History of recurrent implantation failure defined as failed ≥ 2 euploid embryos transfer or ≥ 3 blastocysts

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
Intervention / Treatment
Frozen embryo transfer substituted cycle
In a substituted cycle, estrogen and progesterone are given and a transfer is planned when the endometrium is ready
Other: Frozen embryo transfer
A frozen embryo transfer involves thawing a fertilized embryo and transferring it in the uterus in order to obtain a pregnancy
Frozen embryo transfer natural cycle
In a natural cycle no hormones are given and a transfer is planned when there is a dominant follicle apparent at the ultrasound
Other: Frozen embryo transfer
A frozen embryo transfer involves thawing a fertilized embryo and transferring it in the uterus in order to obtain a pregnancy

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Evaluate the clinical pregnancy rate of embryo transfer in natural vs substituted cycles
Time Frame: 6 to 8 weeks after Frozen Embryo Transfer
clinical pregnancy is the presence of fetal heartbeat at the viability ultrasound
6 to 8 weeks after Frozen Embryo Transfer

Collaborators and Investigators

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

Sponsor

Clinique Ovo

Investigators

  • Principal Investigator: Camille Sylvestre, MD, clinique ovo R&D department

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)

September 19, 2023

Primary Completion (Actual)

November 30, 2023

Study Completion (Actual)

July 18, 2024

Study Registration Dates

First Submitted

September 19, 2023

First Submitted That Met QC Criteria

September 19, 2023

First Posted (Actual)

September 26, 2023

Study Record Updates

Last Update Posted (Estimated)

December 9, 2025

Last Update Submitted That Met QC Criteria

December 3, 2025

Last Verified

December 1, 2025

More Information

Terms related to this study

Other Study ID Numbers

  • 3356

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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