Adequate growth of the endometrium is crucial for implantation. Accordingly, the pregnancy
success rate of patients with a thin endometrium is low. Furthermore, there is a little
information about the factors responsible for impaired endometrial growth in patients with a
thin endometrium. The researches have revealed that nitric oxide (NO) release can cause
relaxation of vascular smooth muscle through a cyclic guanyl monophosphate (cGMP)-mediated
pathway. Sildenafil is a type 5-specific Phosphodiesterase inhibitor that augments the
vasodilatory effects of NO on vascular smooth muscle by preventing the degradation of cGMP
and could improve blood flow and endometrial thickness. This study is designed to evaluate
the effect of vaginally administered sildenafil suppositories on IVF/ICSI outcome of
infertile patients with repeated IVF/ICSI failures.