Participant recruitment and retention in studies investigating pregnancy-related pelvic girdle pain: a methodological systematic review

Abstract Background Recruiting and retaining participants for clinical trials is a common and well-documented challenge, with particular complexity in perinatal populations which are historically underrepresented in health research. Recruitment and retention are known to be shaped by context-specific factors, yet no systematic review has examined these processes within the clinical domain of pregnancy-related pelvic girdle pain (PPGP), a common and potentially debilitating condition affecting around one in five women in the UK. Objective This methodological systematic review aimed to summarise participant recruitment and retention in clinical trials investigating PPGP across four objectives: (1) to identify methods of recruitment and retention; (2) to assess the proportion of target sample size achieved; (3) to assess attrition, including planned allowances and the proportion of participants lost; and (4) to explore potential relationships between recruitment success and relevant variables. Methods A systematic search of seven databases, three trial registries and supplementary searching of additional sources was undertaken from inception. Eligible studies included RCTs, and feasibility and pilot studies preemptive to a future RCT, investigating interventions for women with current or previous PPGP. Data were extracted on recruitment and retention methods and outcomes. A number of supplementary data items were also collected to contextualise the primary outcomes. Study quality was appraised using sections A and B of the CASP RCT checklist. Data were summarised descriptively, using medians and IQRs where appropriate to reflect small numbers and a high degree of data variability. Results Thirty-eight studies published between 2000 and 2025, representing 15 countries, met the inclusion criteria. The most common recruitment methods were via specialist clinics or patient lists and via clinician referral. Only one study reported a retention strategy. Of the 25 studies reporting a recruitment target, 76% achieved or exceeded it and 92% reached at least 90%. Planned attrition allowances were made by 16 studies (median 20%, IQR 13.75–20.75); participant attrition was experienced by 18 studies (median 16.5%, IQR 9.25–24%). Subgroup analyses were broadly homogeneous, with most groups achieving a median of 100% recruitment success. No studies reported participant ethnicity and only nine reported a socioeconomic characteristic. Discussion Recruitment to PPGP trials was generally successful, comparing favourably to broader trends in the UK trial literature. However, substantial gaps in methodological and equity reporting mean that the processes underlying this success remain poorly understood. Subgroup analyses were broadly homogeneous and did not identify clear differential effects by recruitment method, intervention type or natal period; this likely reflects the descriptive and exploratory nature of these analyses and limited reporting detail, rather than a true absence of effect. Future trials would benefit from comprehensive reporting of recruitment and retention methods and the systematic collection of equity-relevant participant characteristics. Trial registration This review was registered on the Open Science Framework on 27 February 2025: https://osf.io/ufr92/files/osfstorage .