Effect of Adding Sildenafil to Protocol of Endometrial Preparation in Outcome of Frozen-thawed Embryo Transfer Cycles

Inclusion Criteria: * women \> 40 years old, * history of endocrine disease * Hysteroscopic surgery * cardiovascular, renal and liver disease * hypotension( blood pressure \< 90/50) * history of stroke or myocardial infarction * use of alcohol or substance Exclusion Criteria: A total of 80 patients with antecedent of poor endometrial response and had frozen embryo included in this study all women must to be \< 40 years old, * no history of endocrine disease, * no Hysteroscopic surgery, had a high quality embryos no cardiovascular, * renal and liver disease and * no hypotension (blood pressure \< 90/50) or * history of stroke or myocardial infarction and * don't use of alcohol or substance Patients with these conditions enter this study and based on randomized tables are divided in two groups.