Large randomized controlled trials in infertility.

As the first paper in this series of Views and Reviews on randomized controlled trials (RCTs), we aim to provide the basics of RCTs in infertility research. In this paper, we discuss the need and ethical considerations of large trials in infertility research and important aspects to guarantee the quality of a trial, including protocols, registrations and monitoring, issues of study design and analysis, and reporting standards. Because most of the treatment effects we would like to study represent relatively small signal-to-noise ratios, large RCTs are required to provide sufficient power to answer these questions. Trial protocols, registrations, and monitoring facilitate the transparency of conduct, analysis, and reporting of the trial. Issues of trial design and analysis, such as nonblinding and misuse of the denominators, are common in published trials in this area and could be further improved. Finally, following the current reporting standard facilitates complete and transparent reporting, critical appraisal, and interpretation.