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Submitted on August 29, 2005
Accepted on November 29, 2005
Division of Reproductive Sciences, Fran and Lawrence Bloomberg Department of Obstetrics & Gynecology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital and The University of Toronto, Toronto, Ontario, Canada; Division of Reproductive Endocrinology & Infertility, Department of Obstetrics & Gynecology, Wayne State University, Detroit, Michigan, USA
* To whom correspondence should be addressed. E-mail: rfcasper{at}aol.com.
Context: For the last 40 yr, the first line of treatment for anovulation in infertile women has been clomiphene citrate (CC). CC is a safe, effective, oral agent but is known to have relatively common antiestrogenic endometrial and cervical mucous side effects that could prevent pregnancy in the face of successful ovulation. In addition, there is a significant risk of multiple pregnancy with CC compared with natural cycles. Because of these problems, we proposed the concept of aromatase inhibition as a new method of ovulation induction that could avoid many of the adverse effects of CC. The objective of this review was to describe the different physiologic mechanisms of action for CC and AIs, and to compare studies of efficacy for both agents for ovulation induction.
Evidence Acquisition: We conducted a systematic review of all the published studies, both controlled and non-controlled, comparing CC and AI treatment, either alone or in combination with gonadotropins, for ovulation induction or augmentation, identified through the Entrez-PubMed search engine.
Evidence Synthesis: Because of the recent acceptance of the concept of using AIs for ovulation induction, few controlled studies were identified and the rest of the studies were pilot or preliminary comparisons. Based on these studies, it appears that AIs are as effective as CC in inducing ovulation, are devoid of any antiestrogenic side effects, result in lower serum estrogen concentrations, and are associated with good pregnancy rates with a lower incidence of multiple pregnancy than CC. When combined with gonadotropins for assisted reproductive technologies, AIs reduce the dose of follicle stimulating hormone (FSH) required for optimal follicle recruitment and improve the response to FSH in poor responders.
Conclusions: Preliminary evidence suggests that AIs may replace CC in the future because of similar efficacy with a reduced side-effect profile. Although worldwide experience with AIs for ovulation induction is increasing, at present, definitive studies in the form of randomized controlled trials comparing CC with AIs are lacking.
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