Overdiagnosis in screening for gestational diabetes: A scoping review

Background: Screening for gestational diabetes mellitus (GDM) in healthy pregnancies is disputed, and rising GDM incidence calls for an investigation into the potential for overdiagnosis. Aim: To identify and map empirical evidence on overdiagnosis in GDM screening and explore how different screening strategies impact overdiagnosis. Methods: This review adheres to the JBI Manual and PRISMA-ScR guidelines. Systematic searches were performed on September 10th, 2024, without date, language, or geography restrictions, in Medline, Embase, CINAHL, Cochrane Library, and Web of Science. One search targeted studies explicitly addressing overdiagnosis through primary empirical analyses, while a second search included RCTs evaluating GDM screening programmes. Evidence screening and selection were carried out independently by two authors. Findings: We included ten studies with varying designs in Search 1 and nine RCTs in Search 2. In Search 1, only one study defined overdiagnosis. In Search 2, seven of nine RCTs show an increased incidence with intensified screening. Of these, six evaluated universal screening and showed no accompanying benefits, suggesting overdiagnosis. Variations in strategies and outcomes complicate comparisons. Additionally, no RCTs compare screening to no screening or risk-based to universal screening, raising uncertainties about the effects of different screening programmes and practices. Discussion: Our analysis of RCT data demonstrates that intensifying screening led to increased incidence without corresponding beneficial effects, indicating overdiagnosis. Few studies have assessed overdiagnosis empirically, and no established framework currently guides the definition or operationalisation of overdiagnosis in GDM screening research. Conclusion: Data from RCTs indicate overdiagnosis in universal GDM screening.