Letrozole

The goal of this randomized clinical trial is to evaluate the effectiveness of the letrozole-stimulated cycle strategy versus the artificial cycle strategy for endometrial preparation in women with irregular menstrual cycles after one cycle of endometrial preparation. The primary question it aims to answer is: • Does the letrozole-stimulated cycle strategy for endometrial preparation result in a higher live birth rate compared to the artificial cycle strategy in women with irregular menstrual cycles after one cycle of endometrial preparation? Participants will undergo screening before endometrial preparation for frozen embryo transfer, following which they will be randomly assigned to one of two groups: LETS or AC. In the LETS group, investigators will prescribe letrozole 5 milligrams/day for 5 days to stimulate follicular development and micronized progesterone 800 milligrams/day for luteal phase support. In contrast, the AC group will receive oral estradiol valerate 6-12 milligrams/day and micronized progesterone 800 milligrams/day. Researchers will compare the LETS and AC groups to determine if there are differences in live birth rates.

This randomized controlled trial (RCT) aims to evaluate whether, in infertile women with WHO II/IV ovulatory disorders, a combination of letrozole (LE) and clomiphene citrate (CC) compared to LE alone, result in higher live birth rates. The study is designed as an open-label, multicenter RCT across six fertility clinics in Vietnam. Participants will be randomized into two groups: (1) LE + CC , (2) LE alone. The primary outcome measure is the live birth rate after one treatment cycle. Based on prior data, the live birth rate for IUI in letrozole cycles is estimated at 12%. To detect a 10% increase in live birth rates with CC, 436 couples are needed (α = 0.05, power = 80%). Additionally, the live birth rate after IUI with LE-induced ovulation is approximately 18.7% (Diamond et al., 2015). To detect a 10% increase with CC, 560 couples are required (α = 0.05, power = 80%). Considering a 5% loss to follow-up and protocol deviations, the study plans to recruit 600 participants (150 per arm).

The goal of this single center, non-blinded, randomized controlled clinical trial to comparison of pregnancy outcomes and perinatal outcomes in patients undergoing IVF treatment (including ICSI) with FET with letrozole-induce endothelial preparation protocol versus natural cycles, hormone replacement protocol. The main questions it aims to answer are: * To investigate whether letrozole-induce endothelial preparation is effective in improving the live birth rate and clinical pregnancy rate. * To explore its possible impact on clinically important indicators such as spontaneous abortion rate, implantation cycle cancellation rate, days of endothelial preparation, and number of visits to the clinic. The study subjects were randomized into groups starting at D1-D3 of the menstrual cycle. The study subjects were stratified according to whether their menstrual cycles were regular or not, and were divided into the following endothelial preparation regimens according to the pre-prepared stratified zoned randomized group numbers: (1) regular menstrual cycles (25-35 d): letrozole ovulation-promoting cycles, natural cycles, and hormone-replacement cycles; and (2) irregular menstrual cycles (\<25 d or \>35 d): letrozole ovulation-promoting cycles, hormone-replacement cycle.