Control group
The women were treated with estradiol valerate tablets (Bayer, Guangzhou, China) 2 mg/day orally starting on the fifth day of the menstrual cycle. If the EMT was measured by transvaginal ultrasound on ovulation day > 7 mm, the intake of estradiol valerate tablets was stopped, and only dydrogesterone 10 mg/day orally (Abbott Biologicals B.V., Netherlands) was used. If EMT on ovulation day remained< 7 mm, the treatment with estradiol valerate tablets was continued and, at the same time, dydrogesterone 10 mg/day orally was added (so-called “sequential hormone replacement therapy”).