In vitro fertilization treatments with the use of clomiphene citrate or letrozole.

There has been increasing interest in combining the oral agents clomiphene citrate (CC) and letrozole with gonadotropins in IVF: for poor responders to reduce the amount of gonadotropins used, and in normal responders to reduce the incidence of ovarian hyperstimulation (OHSS). In normal responders, mild stimulation with the use of CC and gonadotropins was found to decrease the number of oocytes retrieved and result in good pregnancy rates, but in most studies the cumulative pregnancy rate was lower compared with conventional ovarian stimulation when frozen embryo transfers were considered. Coadministration of letrozole and gonadotropins has mainly been used in patients with breast cancer to prevent the massive elevation of serum E2 concentrations with the use of standard controlled ovarian hyperstimulation. CC and letrozole have both been used with gonadotropins in poor responders and have been shown to reduce the amount of gonadotropin used without reducing the pregnancy rate. Letrozole use with gonadotropins in IVF cycles may increase endometrial receptivity by increasing integrin expression in the endometrium and by lowering estrogen concentrations to more physiologic levels.