Early Sonographic Markers of Gestational Diabetes Mellitus: A Narrative Review of Placental, Fetal and Uterine Artery Findings

Background/Objectives: Gestational diabetes mellitus (GDM) is one of the most common metabolic complications of pregnancy and is associated with adverse maternal and neonatal outcomes. Current screening strategies are generally performed during the end of the second trimester, limiting opportunities for early intervention. Increasing evidence suggests that placental and fetal ultrasound markers detectable in early pregnancy may reflect the pathophysiological changes preceding the clinical diagnosis of GDM. This narrative review aims to summarize the current evidence regarding first- and second-trimester placental and fetal ultrasound markers associated with the subsequent development of GDM. Methods: A narrative review of the literature was conducted focusing on studies evaluating ultrasound markers of placental morphology, placental vascularization and function, uterine artery Doppler indices, placental volume, placental thickness, and fetal biometric and functional parameters in relation to later GDM diagnosis. Twenty-two studies were identified and analyzed to assess their clinical utility and predictive value. Results: Increasing evidence suggests that placental and fetal ultrasound markers detectable in early pregnancy may reflect pathophysiological changes preceding the clinical diagnosis of GDM. Three-dimensional power Doppler, particularly the vascularization–flow index, has demonstrated reduced placental vascularization in pregnancies subsequently complicated by GDM. Placental elastography and artificial intelligence-based radiomic analysis also show promising predictive potential. Uterine artery Doppler has demonstrated limited and inconsistent value. Fetal findings suggest that conventional biometry has limited predictive utility, whereas fetal growth velocity and markers of adiposity, including anterior abdominal wall thickness and abdominal overgrowth, more consistently identify early adaptations associated with later GDM. However, substantial methodological heterogeneity limits interpretation. Conclusions: Early placental and fetal ultrasound markers represent promising non-invasive tools for the early identification of pregnancies at risk for GDM. Further large-scale prospective studies are required to validate their predictive performance and establish standardized assessment protocols. Integrating maternal clinical characteristics and biochemical parameters may enhance future screening strategies for GDM.