IRCT201210232575N3 IRCT 2012-12-24 Yazd Shahid Sadoughi University of Medical Sciences and Health Services, Vice Chancellor for resear Effect of sildenafil citrate on endometrial preparation and on the outcome of the frozen-thawed embryo transfer cycles Effect of sildenafil citrate on endometrial preparation and on the outcome of the frozen-thawed embryo transfer cycles in infertile women: a clinical trial 2009-03-20 anticipated 80 Complete https://irct.ir/trial/2325 interventional Randomization: Randomized, Blinding: Not blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment. 2 Female Infertility. Intervention 1: For group I start 2mg estradiol valerat (tablet) from first to 4th day of the menstrual cycle, and continue by 4mg from 5th to 8th day, and 6mg from 9th to 20th day of the menstrual cycle. In 13th day of the menstrual cycle endometrial thickness estimated with transvaginal ultrasonography (arranged in a series every other day), evaluations were performed by a single investigator, if the endometrial thickness is more than 8mm, 100 mg progesterone injected intramuscular and after three days embryo was transferred. Estradiol valerat and progesterone continued until two weeks after embryo transferred, then BHCG tested. If BHCG is positive, estradiol valerat and progesterone continues until 11 weeks of pregnancy . Then four weeks after the embryo transfer, the number of gestational sac are determined by vaginal ultrasound. Intervention 2: In the group II in addition to the above treatment protocol, from first day of cycle until the day of starting progesterone will be given 50mg sildenafil citrate tablets daily and it was discontinued between 48-72 hours previous of the embryo transfer. In 13th day of the menstrual cycle endometrial thickness estimated with transvaginal ultrasonography (arranged in a series every other day), evaluations were performed by a single investigator, if the endometrial thickness is more than 8mm, 100 mg progesterone injected intramuscular and after three days embryo was transferred. Estradiol valerat and progesterone continued until two weeks after embryo transferred, then BHCG tested. If BHCG is positive, estradiol valerat and progesterone continues until 11 weeks of pregnancy . Then four weeks after the embryo transfer, the number of gestational sac are determined by vaginal ultrasound.