Metformin versus clomiphene citrate for infertility in non-obese women with polycystic ovary syndrome: a systematic review and meta-analysis

Abstract

BACKGROUND: Recent studies suggest that metformin may be more effective in women with polycystic ovary syndrome (PCOS) who are non-obese. The objective here is to determine and compare the effectiveness of metformin and clomiphene citrate for improving fertility outcomes in women with PCOS and a BMI, 32 kg/m2 (BMI 32 kg/m2 was used to allow for international differences in BMI values which determine access to infertility therapy through the public health system). METHODS: Databases were searched for English language articles until July 2011. Inclusion criteria: women of any age, ethnicity and weight with PCOS diagnosed by all current criteria, who are infertile; at least 1000 mg of any type of metformin at any frequency, including slow release and standard release, compared with any type, dose and frequency of clomiphene citrate. Outcomes: rates of ovulation, live birth, pregnancy, multiple pregnancies, miscarriage, adverse events, quality of life and cost effectiveness. Data were extracted and risk of bias assessed. A random effects model was used for meta-analyses of data, using risk ratios (relative risk). RESULTS: The search returned 4981 articles, 580 articles addressed metformin or clomiphene citrate and four randomized controlled trials (RCTs) comparing metformin with clomiphene citrate were included. Upon meta-analysis of the four RCTs, we were unable to detect a statistically significant difference between the two interventions for any outcome in women with PCOS and a BMI , 32 kg/m2, owing to significant heterogeneity across the RCTs. CONCLUSIONS: Owing to conflicting findings and heterogeneity across the included RCTs, there is insufficient evidence to establish a difference between metformin and clomiphene citrate in terms of ovulation, pregnancy, live birth, miscarriage and multiple pregnancy rates in women with PCOS and a BMI , 32 kg/m2. However, a lack of superiority of one treatment is not evidence for equivalence, and further methodologically rigorous trials are required to determine whether there is a difference in effectiveness between metformin and placebo (or no treatment) or between metformin and clomiphene citrate for ovulation induction in women with PCOS who are non-obese. Until then, caution should be exercised when prescribing metformin as first line pharmacological therapy in this group of women.