Comparison of pregnancy outcome after letrozole versus clomiphene treatment for mild ovarian stimulation protocol in poor responders

Background: Poor ovarian response to controlled ovarian stimulation is one of the most important interest points in assisted reproduction. Mild ovarian stimulation seems to be preferable to high dose of FSH regimens in women with a history of poor ovarian response in previous protocol. Clomiphene citrate and letrozole alone or in combination with FSH have been used in mild ovarian stimulation protocol.
Objective: To compare the efficacy of letrozole and clomiphene citrate for mild ovarian stimulation on assisted reproductive technology outcomes in poor responders.
Materials and Methods: In a randomized control study, 184 women aged between 20 and 45 years with the history of poor response to ovarian stimulation who were candidate for ART were randomly subdivided into two groups: group I (n= 80), women who underwent the clomiphene/gonadotropin/antagonist protocol; and group II (n= 87), patients who underwent the letrozole/gonadotropin/antagonist protocol. Groups were compared regarding implantation, chemical and clinical pregnancy rates.
Results: There was a significant difference in the mean endometrial thickness between two groups (9.16±1.2 mm vs. 8.3±0.3 mm). The implantation rate was significantly higher in letrozole group compare to clomiphene group (7.2 vs. 6.6%, p=0.024 respectively). No significant differences were found in chemical and clinical pregnancy rate between two groups.
Conclusion: In mild ovarian stimulation protocol, letrozole and clomiphene have similar value for the poor responder. The optimal treatment strategy for these patients remains debated.

Keywords
Clomiphene; Letrozole; Mild ovarian stimulation protocol; Poor responders