Twenty years of Cochrane reviews in menstrual disorders and subfertility.

The past three decades have seen considerable change in the understanding of clinical research methods. There has been an acceptance that RCTs are the best way of establishing treatment effectiveness and a recognition that, while single studies are useful, pooling knowledge from a complete body of work is likely to provide the best evidence. Advances in methodology have been mirrored by the many advances in the field of reproductive medicine, such as assisted reproduction, assessment of male fertility, ovulation induction and laparoscopic surgery. Together, they have led to welcome improvements in the outcomes of fertility treatments. In particular, systematic reviews have become important tools enabling clinicians and patients to make health-care decisions based on evidence from all the available high-quality studies. The move towards identifying and aggregating the highest quality evidence has been led by the Cochrane Collaboration, which this year celebrates 20 years of preparing and publishing systematic reviews. This paper outlines the achievements, progress and challenges of this enterprise to date, with a particular focus on systematic reviews of reproductive medicine.