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.