Progression to type 2 diabetes mellitus after gestational diabetes: An umbrella review of 15 systematic reviews and assessment of causal frameworks

Gestational diabetes mellitus (GDM) confers a markedly elevated risk of progression to type 2 diabetes mellitus (T2DM), although the precise magnitude of this risk and its temporal evolution remain inadequately characterized for clinical decision-making. To systematically synthesize reviews on glycemic alterations following GDM, quantifying prevalence, incidence, and risk estimates, and to critically assess the use of causal frameworks for inference regarding risk factors. We conducted an umbrella review with searches in PubMed/MEDLINE, Embase, Web of Science, and Scopus through September 2025. For reviews that synthesized risk factors, we assessed whether they employed directed acyclic graphs to guide adjustment for confounders. Fifteen reviews with data from more than 3 million women were included. Prior GDM conferred a 6- to 13-fold increased risk of T2DM compared with normoglycemic pregnancies, with cumulative incidence of 9–32 % depending on ethnicity, follow-up duration, and diagnostic criteria. The incidence rate was 26.20 per 1000 person-years, projecting to 20 % at 10 years. Twenty-seven percent presented glycemic alterations at 6–12 weeks postpartum. The most consistent predictors included glycemic markers during pregnancy, insulin requirement, elevated body mass index, family history, and non-White ethnicity. Critically, no review employed directed acyclic graphs to support confounder adjustment, introducing substantial risk of residual bias in the reported point estimates, although the direction of associations showed robust consistency across temporal windows and independent reviews. GDM substantially increases T2DM risk, with glycemic burden evident from early postpartum. The universal absence of DAGs limits causal inference regarding point estimates, although the direction of associations is robust. • Gestational diabetes confers a 6–13 fold increased risk of type 2 diabetes compared to controls. • 27% of cases present dysglycemia at 6–12 weeks postpartum, marking a critical screening window. • Predictors: high BMI, insulin use, elevated glycemic markers, and diabetes family history. • No review used directed acyclic graphs (DAGs), limiting causal interpretation of risk factors. • Universal postpartum screening is justified, utilizing immediate hospitalization strategies.