الفهرس 
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Abstract
The successful pregnancy requires adequate endometrial thickness and receptivity in the cycles of ovulation induction. An inadequate endometrium can be considered as a main fertility-determining factor. Clomiphene citrate is one of selective estrogen receptor modulators.
Clomiphene citrate has anti-estrogenic effect on endometrial development and receptivity, leads to diminish endometrial blood flow in clomiphene-induced cycle. Sildenafil citrate is a specific type of phosphodiesterase inhibitor 5, improves the vasodilatation effects of nitric oxide (NO) on blood vessels and smooth muscle by blocking cGMP breakdown. Sildenafil citrate boosts estrogen-induced endometrial growth and may improve uterine blood flow.
A prospective study evaluated the efficacy of using vaginal sildenafil citrate with clomiphene in PCOS patients, was conducted on 80 female (PCOS) patients. The patients were divided into two groups: one group received clomiphene and sildenafil transvaginal, and the other group received clomiphene alone.
The study showed a statistically significant improvement in endometrial thickness and number of dominant follicles in sildenafil group and also, increase pregnancy rate in sildenafil group with no significant difference between the two studies groups.
The current study recommends the use of vaginal sildenafil citrate for the improvement thickness of endometrium and pregnancy rate with clomiphene during ovulation induction. Adding sildenafil citrate to the clomiphene citrate regimen for patients with PCOS improves endometrial thickness and pregnancy rate.