An interventional study of Letrozole (Aromatase Inhibitors) and Choriogonadotropin alpha (r-hCG) in Infertility Female and Frozen Embryo Transfer (FET), sponsored by University of Novi Sad. Recruiting at 1 site in Serbia. Open to female participants aged 18 Years to 40 Years. Per ClinicalTrials.gov, last updated 2026-09-29.
Sponsored by University of Novi Sad · Not applicable, Interventional, and Treatment
The goal of this clinical trial is to learn whether different natural approaches to preparing the uterus for frozen embryo transfer (FET) can improve pregnancy success in women undergoing in vitro fertilization (IVF) treatment.
The main questions it aims to answer are:
Researchers will compare four different approaches to see which one results in the highest chance of achieving a clinical pregnancy, confirmed by ultrasound.
Participants will:
540 studies on the registry are indexed under Infertility, Female; 138 are open to participants now.
This study's planned enrollment of 120 is above the median of 100 across 371 interventional studies indexed under Infertility, Female.
Browse Infertility, Female studies →University of Novi Sad is the lead sponsor of 26 studies on the registry; 7 are open to participants now.
Counted across the registry records on this site, refreshed daily.
Exclusion Criteria:
Participants undergo frozen embryo transfer in a true natural menstrual cycle without the use of either an aromatase inhibitor or ovulation trigger medication. Ovulation is monitored by ultrasound and serum hormone levels. Luteal phase support (vaginal progesterone 200 mg twice daily or subcutaneous progesterone 25 mg once daily) is initiated on the day of ultrasound-confirmed ovulation and continued until 12 weeks of gestation if pregnancy occurs.
Drug: Progesterone
Participants undergo frozen embryo transfer (FET) in a true natural menstrual cycle with administration of the aromatase inhibitor letrozole (2.5 mg twice daily) from cycle days 3-7. Ovulation is monitored by ultrasound and serum hormone levels. Luteal phase support (vaginal progesterone 200 mg twice daily or subcutaneous progesterone 25 mg once daily) is initiated on the day of ultrasound-confirmed ovulation and continued until 12 weeks of gestation if pregnancy occurs.
Drug: Letrozole (Aromatase Inhibitors) · Drug: Progesterone
Participants undergo frozen embryo transfer in a modified natural menstrual cycle without the use of an aromatase inhibitor. When the dominant follicle reaches ≥17 mm and endometrial thickness is ≥7 mm, and after exclusion of a spontaneous LH surge by serum measurement, ovulation is triggered with recombinant human chorionic gonadotropin (hCG) 250 mcg. Luteal phase support (vaginal progesterone 200 mg twice daily or subcutaneous progesterone 25 mg once daily) is initiated 2 days after ovulation trigger and continued until 12 weeks of gestation if pregnancy occurs.
Drug: Choriogonadotropin alpha (r-hCG) · Drug: Progesterone
Participants undergo frozen embryo transfer (FET) in a modified natural menstrual cycle with administration of letrozole (2.5 mg twice daily) from cycle days 3-7. Ultrasound monitoring begins between cycle days 8-10. When the dominant follicle reaches ≥17 mm and endometrial thickness is ≥7 mm, and after exclusion of a spontaneous LH surge by serum LH measurement, ovulation is triggered with recombinant human chorionic gonadotropin (hCG) 250 mcg. Luteal phase support (vaginal progesterone 200 mg twice daily or subcutaneous progesterone 25 mg once daily) is initiated 2 days after ovulation trigger and continued until 12 weeks of gestation if pregnancy occurs.
Drug: Letrozole (Aromatase Inhibitors) · Drug: Choriogonadotropin alpha (r-hCG) · Drug: Progesterone
Letrozole 2.5 mg administered orally twice daily from cycle days 3-7 during the early follicular phase.
Recombinant human chorionic gonadotropin (hCG) 250 mcg administered subcutaneously to trigger ovulation when follicular and endometrial criteria are met.
Luteal phase support with either vaginal progesterone 200 mg twice daily or subcutaneous progesterone 25 mg once daily, initiated after ovulation (or 2 days after hCG trigger) and continued until 12 weeks of gestation if pregnancy occurs.
Clinical Pregnancy Rate
Number of pregnancies with an ultrasound-confirmed gestational sac per embryo transfer.
Time frame: Approximately 4-6 weeks after embryo transfer.
Biochemical Pregnancy Rate
Number of pregnancies with elevated serum beta-human chorionic gonadotropin (β-hCG) levels measured two weeks after embryo transfer, per embryo transfer.
Time frame: Two weeks after embryo transfer.
Implantation Rate
Number of ultrasound-confirmed gestational sacs divided by the number of embryos transferred.
Time frame: Approximately 4-6 weeks after embryo transfer.
Miscarriage Rate
Pregnancy loss before 23 completed weeks of gestation, expressed per embryo transfer.
Time frame: Up to 23 weeks of gestation.
Plan to share: No
No publications or documents are linked to this record.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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University of Novi Sad