Gestational Dysglycemia as a Continuum: A Systematic Review Integrating Continuous Glucose Monitoring, Insulin Resistance, and Placental Metabolic Signals

Introduction: Gestational diabetes mellitus has traditionally been approached as a binary diagnosis, defined by glucose thresholds applied at a single point in midpregnancy. Yet, clinical experience and emerging evidence increasingly suggest that maternal glucose regulation during pregnancy behaves less like a switch and more like a spectrum. Rather than an isolated diagnostic event, pregnancy is characterized by progressive metabolic adaptation, graded insulin resistance, and placental signaling that evolve over time. Methods: In this systematic review, we searched major biomedical databases and registers from inception to the most recent search, and synthesized current evidence reframing gestational dysglycemia as a continuous metabolic spectrum, shaped by dynamic glucose patterns, progressive insulin resistance, and active placental signaling, following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidance. Results: We identified 1246 records, of which 31 studies met predefined inclusion criteria. The included literature encompassed observational cohorts, interventional studies, mechanistic investigations, and narrative or systematic reviews, spanning continuous glucose monitoring, insulin resistance phenotyping, placental biomarkers, and pregnancy outcomes across diverse populations. Rather than focusing solely on diagnostic cutoffs, the included literature consistently points to graded associations between glycemic exposure – captured through mean glucose, variability, and time above pregnancy-specific ranges – and adverse maternal and fetal outcomes. Evidence from early gestation further implicates placental endocrine and inflammatory pathways as contributors to dysglycemia well before conventional screening windows. Synthesizing these findings, we observe that clinically relevant risk often emerges below current diagnostic thresholds and evolves dynamically over time, challenging the adequacy of binary screening frameworks. Conclusion: Viewing gestational dysglycemia as a spectrum has implications for earlier risk stratification, more individualized surveillance, and a life-course perspective on maternal and offspring metabolic health. Ultimately, the findings support a shift from threshold-based classification toward a more nuanced, physiology-driven understanding of glucose regulation in pregnancy, aligned with contemporary tools and biological insight. This review does not advocate abandoning existing diagnostic criteria; instead, it proposes situating threshold-based definitions within a broader conceptual framework that acknowledges continuity, biological heterogeneity, and timing.