Late Onset Gestational Diabetes Mellitus: Clinical Implications of Delayed Diagnosis and a Pragmatic Approach to Screening: A Narrative Review

Abstract

Background Gestational diabetes mellitus (GDM) increases maternal and neonatal risks and its reported prevalence has risen with evolving diagnostic criteria and screening strategies. Although screening at 24–28 weeks is widely recommended, optimal testing methods and the value of screening outside that window remain contested. The aim of this narrative review is to critically examine the clinical significance, epidemiology, and pragmatic screening strategies for GDM first identified or retested in late pregnancy (the third trimester) after normal midpregnancy screening. Methods This narrative synthesis integrates findings from observational studies, retrospective cohorts, guideline statements, and relevant systematic reviews (including a 2024 meta‐analysis) to summarize current knowledge and highlight gaps. Results Reports show that repeat testing can detect new GDM cases. For example, one published retrospective cohort reported an 18.3% incidence among high‐risk women retested in the third trimester. Observational evidence and published reviews indicate associations between late‐diagnosed GDM and higher rates of shoulder dystocia, cesarean delivery, and low 5‐min Apgar scores, though findings for macrosomia, neonatal hypoglycemia, and NICU admission are inconsistent. The short interval between late diagnosis and delivery limits the potential impact of interventions, and diagnosis itself may increase medicalization. Standard IADPSG OGTT thresholds were derived from 24–32‐week cohorts and their applicability in later gestation is uncertain. Pragmatic, selective strategies—targeted retesting based on ultrasound or clinical risk, or screening with random glucose/HbA1c to detect overt hyperglycemia—may reduce unnecessary OGTTs while identifying clinically meaningful cases. Conclusions As a narrative review, this article synthesizes current evidence to conclude that late‐onset GDM is clinically relevant but understudied; universal third‐trimester OGTT is not yet supported by robust outcome data. Prospective studies are needed to define optimal screening populations, diagnostic criteria, and management in late pregnancy.