FET-LET-2x2: Clinical Pregnancy Rates After Frozen Embryo Transfer in Natural and Modified Natural Cycles

What Was Tested

This registered not phased trial tested hCG (human chorionic gonadotropin).

The main questions it aims to answer are: 1.

Is a completely natural menstrual cycle more successful than a natural cycle in which ovulation is triggered with medication when preparing for frozen embryo transfer? 2.

It had four arms (groups): True Natural Cycle Without Letrozole (experimental), True Natural Cycle With Letrozole (experimental), Modified Natural Cycle Without Letrozole (experimental) and Modified Natural Cycle With Letrozole (experimental).

The registry classes the interventions as drug.

Who Took Part

The registry lists 120 planned participants were the target.

It was open to women only aged from 18 years up to 40 years.

Healthy volunteers were not accepted; participants needed the condition being studied.

Examples of who could join: Women aged 18 to 40 years. Regular menstrual cycles (26-35 days). Scheduled for frozen embryo transfer (FET) in a natural menstrual cycle. Ability to provide written informed consent.

The full record lists 5 inclusion and 6 exclusion criteria; among the exclusions: use of preimplantation genetic testing (pgt) for the transferred embryo; use of donor oocytes; irregular menstrual cycles.

How the Study Was Run

The set-up was randomized, factorial and open-label.

Random assignment meant chance, not the researchers, decided who got hCG (human chorionic gonadotropin) and who got the comparison, which limits bias.

Being open-label, the hCG (human chorionic gonadotropin) study did not mask who received what.

It started in 2026-03-13 with completion listed for 2027-02.

It ran at 1 site in Serbia.

Its stated primary purpose is treatment.

What Was Measured

Researchers chose this as the main measure: Clinical Pregnancy Rate (time frame: Approximately 4-6 weeks after embryo transfer).

It also tracked 3 secondary outcomes, for example Biochemical Pregnancy Rate, Implantation Rate and Miscarriage Rate.

What This Means in Plain Language

Put simply, this is a not phased, randomized trial of hCG (human chorionic gonadotropin) in 120 people.

It is still recruiting; no results are posted to the registry yet, so nothing here describes outcomes.

More context: the hCG (human chorionic gonadotropin) compound page, all human trials.