[Article] The contribution of sildenafil (Viagra) to ovarian stimulation with gonadotropins in a woman with poor ovarian response Eftihios Trakakis,Vassilios Vaggopoulos,Vasileios D. Sioulas,Periklis Panagopoulos,Ioannis Grammatikakis,Peny Ambatzi &Dimitrios Kassanos