Objectives: Transparent trial conduct requires prospective registration of a randomized controlled clinical trial (RCT) before the enrollment of the first participant. We aimed to (1) estimate the proportion of RCTs that are prospectively registered and analyze the time trends and factors linked to registration timing and (2) assess the reasons for nonadherence to prospective registration and explore ways to improve compliance. We studied trials published in rheumatology as a case study.

Study design and setting: We searched for RCTs in rheumatology published between 2009 and 2022. We conducted a multivariable logistic regression to identify factors associated with prospective trial registration. We sent a survey to investigators of trials not prospectively registered, asking about reasons for nonadherence and potential solutions.

Results: We identified 1093 RCTs; 453 (41.4%) were not prospectively registered. Of these, 130 (11.9%) were not registered and 323 (29.5%) were retrospectively registered. Prospective registration increased by 3% annually (P < .001), with 13.3% (2 of 15) trials registered in 2009 to 73.2% (112 of 153) in 2022. In journals supporting the International Committee of Medical Journals Editors recommendations, 16% of trials published in 2022 were not prospectively registered. Prospective registration was associated with a larger sample size, multinational recruitment, and publication in higher impact journals. Investigators reported lack of knowledge or organizational problems as key reasons for retrospective registration. They suggested linking ethical approval to trial registration to ensure prospective registration.

Conclusion: Despite significant improvement, adherence to prospective registration remains unsatisfactory in rheumatology. Targeted strategies for journal editors, health-care professionals, and researchers may help improve trial registration.