Comparison of Progesterone-modified Natural Cycle and Hormone Replacement Therapy Cycle for Endometrial Preparation in Single Frozen Blastocyst Transfer

On days 8-12 of the menstrual cycle (MC), depending on the length of the patient's MC, transvaginal ultrasound is used to monitor follicular development and endometrial growth. Vaginal micronized progesterone (Utrogestan, Besins, Belgium) is started at 200 mg in the afternoon and 200 mg in the evening when the dominant follicle reached ≥16 mm and the endometrial thickness is at least 7 mm. A blastocyst is transferred on day 5 after the addition of progesterone. On day 14 after blastocyst transfer, serum β-hCG levels are measured. Upon positive serum pregnancy testing, progesterone support will continue until 8-10 weeks of gestation. However, afternoon progesterone use is eliminated for 30 days after embryo transfer.

Endometrial preparation will begin on the second day of the menstrual cycle with oral estradiol (E2) valerate at a dose of 2 mg twice daily. When the patient's endometrial thickness is ≥7 mm, vaginal progesterone administration will be initiated at a dose of 200 mg 3 times daily. On day 5 of the progesterone administration, blastocysts are thawed and transferred. For patients with endometrial thickness <7 mm, patients continued oral E2 until the endometrium is ≥7 mm. On day 14 after blastocyst transfer, serum β-hCG levels are measured. Upon positive serum pregnancy testing, E2 and progesterone supplementation is continued for 8-10 weeks of gestation.