Compliance with prospective trial registration guidance remained low in high-impact journals and has implications for primary end point reporting.

Objectives: To examine compliance with International Committee of Medical Journal Editors' (ICMJE) policy on prospective trial registration along with predictors of compliance.

Study Design And Setting: Cross-sectional analysis of all articles reporting trial results published in the six highest-impact general medicine journals in January-June 2014 that were registered in a public trial registry. The main outcome measure was compliance with ICMJE policy. The time frame for trial primary end point ascertainment was used to assess whether retrospective registration could have allowed changing of primary end points following an interim analysis.

Results: Forty of 144 (28%) articles did not comply with the ICMJE policy. Trials of non-FDA-regulated interventions were less compliant than trials of FDA-regulated interventions (i.e., medicines, medical devices) (42% vs. 21%; P = 0.016). Twenty-nine of these 40 (72%; 20% overall) were registered before any interim analysis of primary end points could have been conducted; 11 (28%; 8% overall) were registered after primary end point ascertainment, such that investigators could have had the opportunity to conduct an interim analysis before trial registration.

Conclusion: Twenty-eight percent of trials published in high-impact journals were retrospectively registered including nearly 10% that were registered after primary end point ascertainment could have had taken place. Prospective registration should be prompted and enforced to ensure transparency and accountability in clinical research.