Introduction
Randomised controlled trials (RCTs) are considered to be the best strategy in evaluating the effectiveness of medical interventions and they maintain a dominant position in the hierarchy of medical evidence(1). RCT outcomes are most often adopted into (inter) national clinical guidelines and have great influence on daily routine clinical practice. Unfortunately, obtaining evidence from RCTs is often hampered by failure to recruit enough patients within the pre-planned study period, leading to premature termination of the trial or extension of the study period(2).
Premature termination due to poor recruitment has been estimated to occur in 9-10% of all
RCTs(3-5). Variables that have been associated with poor recruitment are an overestimation of the number of eligible patients, a preference for one of the interventions by the patients, a high burden of the tested intervention for the patients, an unclear trial design, strict eligibility criteria, a lack of logistic support or a lack of funding(6-9).
While the variables that may result in poor recruitment leading to premature termination of the trial are well known, much less is known on variables related to recruitment failure within the pre-planned study period, leading to extension of the study period.
The one study to investigate this matter, explored factors associated with recruitment in a cohort of 114 multicentre RCTs in more than nine clinical areas, including cancer, cardiology and obstetrics & gynaecology (18 RCTs had a clinical area classified as ‘other’), and funded by two public bodies in the United Kingdom; the UK Medical Research Council (MRC) and the Health Technology Assessment (HTA) Programme(5). RCTs that were funded by the MRC (as compared with the HTA) and were in the clinical area ‘cancer’, had better chances of good recruitment, which was a marginally statistically significant association. The vast heterogeneity of RCTs included in that study hampered the identification of other indicators associated with poor recruitment and did not allow the authors to provide useful advice for improvement.
A longer recruitment period may result in a shortage of resources possibly impacting the quality of the trial, limit the institutional capacity to start new RCTs, result in a trial that tries to answer a question that is no longer relevant, or result in premature termination of the study, thus hindering a conclusion with sufficient statistical power(10).
To assess factors that are associated with recruitment failure within the pre-planned study period, we performed a nationwide cohort study of RCTs within the setting of the Dutch Consortium of Obstetrics & Gynaecology in the Netherlands. Such knowledge may be instrumental in helping researchers, trial centres and funding agencies to prevent this type of recruitment failure.