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STUDY QUESTION: What is the prevalence and source of prospectively and retrospectively registered and unregistered trials in fertility treatments? SUMMARY ANSWER: Trial registration is low and does not appear to be changing over the 5 years studied. WHAT IS KNOWN ALREADY: Trial registration is associated with lower risk of bias than in unregistered trials. STUDY DESIGN, SIZE, DURATION: The Cochrane Gynaecology and Fertility Group's specialised register was searched on 5 November 2015 for randomised controlled trials (RCTs) published from January 2010 to December 2014. PARTICIPANTS/MATERIALS, SETTING, METHODS: Eligible trials included randomised women or men for fertility treatments, were published in full text, and written in English. Two reviewers independently assessed trial registration status for each trial, by searching the publication, trial registries, and by contacting the original authors. MAIN RESULTS AND ROLE OF CHANCE: Of 693 eligible RCTS, only 44% were registered trials. Of 309 registered trials, 21.7% were prospectively registered, 15.8% were registered within 6 months of first patient enrolment and 62.5% were retrospectively registered trials. Prospective trial registration by country varied from 0% to 100%. The highest frequency of prospective trial registration amongst the top 10 publishing countries was 31% in the Netherlands. LIMITATIONS, REASONS FOR CAUTION: Only English language trials were included in this review. WIDER IMPLICATIONS OF THE FINDINGS: Prospective trial registration is still low. Journals, funders and ethics committees could have a greater role to increase trial registration. STUDY FUNDING/COMPETING INTERESTS: University of Auckland. No competing interests.
Farquhar et al. (Wed,) studied this question.