Study design
All participants were assigned to the intervention or control group according to the random number table on the day of embryo transfer. Each female was enrolled and studied only once. Patients were administered estradiol valerate ranging from 6 to 8 milligrams daily from day 2 or day 3 of the cycle, followed by daily progesterone injections (total dose 80 mg) when the endometrial thickness reached 7mm at least. The thickness of the endometrium was assessed with a transvaginal ultrasound. Transfer of embryos in the cleavage stage on the fourth day after progesterone conversion and blastocysts on the sixth day. The quality of the frozen-thawed embryos was recorded in the data. All embryos were frozen by vitrification and graded according to the Istanbul Global Consensus Scoring System (