Starting at D3 of the menstrual cycle, letrozole 2.5 mg po qd was administered for 5 days. After 1 week, ultrasound was performed to dynamically monitor follicular development, and 75-150 IU im qd of human menopausal gonadotrophin (hMG) given to continue ovulation stimulation as needed, and oestradiol valerate 2 mg po qd was given to regulate endometrial thickness until the follicle developed to 16 mm in diameter and 7 mm in endometrial thickness. The follicles developed to ≥16 mm in diameter and ≥7 mm in lining thickness and were dynamically monitored by ultrasound and serum sex hormone levels to determine the day of ovulation. From the day of ovulation, dexamethasone 10 mg po tid was administered, and cleavage-stage embryos were transferred 2 or 3 days later, or blastocysts were transferred 5 days later. Deferiprone 10 mg po tid was continued for 14 days after transfer.

Follicular development was monitored dynamically by ultrasound from D8-D11of the menstrual cycle until the follicles developed to ≥16 mm in diameter and ≥7 mm in endothelial thickness, and the day of ovulation was determined by dynamic ultrasound monitoring and detection of serum sex hormone levels. Deferiprone 10 mg po tid was administered from the day of ovulation, and D2 or D3 cleavage stage embryos were transferred 2 or 3 days later, or blastocysts were transferred 5 days later. Deferiprone 10 mg po tid was continued for a total of 14 days after transfer. Cycles were canceled if endothelial thickness was <7 mm on the day of ovulation or if serum progesterone levels were 5 nmol/L before ovulation.

Starting from D1-D5 of the menstrual cycle, estradiol valerate 2 mg po bid was administered for 7 days, followed by ultrasound for dynamic monitoring of endothelial and follicular development, and if the endothelial thickness was <7 mm, the dosage of estradiol valerate was increased to 3-4 mg po bid as appropriate. The number of days of hormone replacement ranged from 11-20 days, and when the endothelial thickness was 7 mm, luteinizing hormone vaginal slow-release gel 90 mg pv qd was added, as well as dexedrine and progesterone 10 mg po bid to transform the endothelium 2 or 3 days later or 5 days later. Progesterone 10 mg po bid was added to transform the endothelium, and cleavage stage embryos were transferred 2 or 3 days later, or blastocysts were transferred 5 days later. Luteal support as described above was continued for a total of 14 days after transfer.

Different endothelial preparations according to groups, see arm descriptions for details

The number of deliveries resulting in at least one live birth

Clinical pregnancies diagnosed by ultrasonographic visualisation of gestational sacs, the number of clinical pregnancies expressed per 100 embryo transfer cycles