Temporal Trends and Determinants of Gestational Diabetes Mellitus and Perinatal Outcomes in Tuscany, Italy (2010–2021)

Background: /Objectives: The prevalence of gestational diabetes mellitus (GDM) has in-creased worldwide over recent years. This rise has been attributed to changes in diagnostic criteria and to evolving demographic and metabolic risk profiles. The present study aimed to evaluate temporal trends in GDM prevalence in Tuscany, Italy, from 2010 to 2021, and to assess whether these trends were associated with changes in major risk factors and GDM-associated maternal–neonatal outcomes. Methods: This population-based retrospective study included all singleton pregnancies recorded in regional Delivery Assistance Certificates (CeDAP) registry between 2010 and 2021 filled by midwives at almost every delivery in Tuscany. GDM was identified using vali-dated clinical algorithms, in accordance with IADPSG criteria implemented from 2013. Temporal trends in GDM prevalence, major risk factors (pregestational obesity, maternal age, origin from High Pressure Migration Countries—HPMC, and adverse maternal and neonatal outcomes were analyzed. Multivariate log linear Poisson regression models were used to assess independent asso-ciations and yearly trends after adjustment for confounders. Results: Among 266,394 pregnancies, mean GDM prevalence was 11.37% and increased progressively over time, despite a concomitant decline in birth rates. Parallel increases were observed in pregestational obesity and in pregnancies among women from HPMC. Multivariate analysis found pregestational obesity, older maternal age, and HPMC ethnicity as the main factors driving the rise in GDM prevalence over time. Ce-sarean deliveries and fetal macrosomia decreased over time, whereas preterm birth increased among GDM pregnancies. Adverse maternal and neonatal outcomes were more strongly associat-ed with pregestational obesity and maternal age than with GDM itself. Conclusions: A true in-crease in GDM prevalence occurred in Tuscany between 2010 and 2021, primarily driven by rising pregestational obesity, advanced maternal age, and HPMC migration. Fetal macrosomia, cesarean delivery, and neonatal distress, were primarily associated with pregestational obesity and mater-nal age, rather than GDM itself. These findings highlight the importance of preventive strategies targeting metabolic health before pregnancy and support the effectiveness of organized GDM screening and management in reducing adverse outcomes.