Systematic review and meta-analysis of letrozole and clomiphene citrate in polycystic ovary syndrome

Major databases were searched for eligible randomised controlled trials (RCTs). The methodological quality of the included studies was assessed by two independent reviewers. Meta-analysis was performed using random-effect model to account for the high levels of heterogeneity. Overall, ten eligible RCTs involving 1905 women were included. Letrozole was associated with significantly higher ovulation rate (relative risk (RR) 1.20; 95% CI 1.03-1.40; P = 0.02); clinical pregnancy rate (RR 1.48; 95% Cl 1.12-1.94; P = 0.005) and endometrial thickness (standardized mean difference (SMD) 2.31; 95% Cl 0.85-3.76; P = 0.002). There was no evidence of a difference between the treatment groups in the rate of miscarriage, number of mature follicles and multiple pregnancy rates. The result suggests that letrozole is a superior ovulation induction agent for women with PCOS as it is associated with higher ovulation and clinical pregnancy rates with no obvious increased side effects. However, this conclusion should be considered with a slight caution in that the quality of the evidence could have improved if more recent studies on the subject were available to be included in the review.