Early Gestational Diabetes Mellitus Diagnosis: A Strategy for Mitigating Excessive Maternal Weight Gain—LINDA-Brasil Study

<b>Background/Objectives</b>: While clinical guidelines recommend screening and treatment for gestational diabetes mellitus (GDM) between 24 and 28 weeks, the benefits of earlier diagnosis are emerging. The objective of this study was to evaluate whether the early diagnosis of GDM is associated with reduced excessive gestational weight gain (GWG). <b>Methods:</b> Cohort study that analyzed 4694 pregnant women diagnosed with GDM attending high-risk prenatal care services within the Brazilian Unified Health System in six Brazilian capitals. GWG was classified according to Brazilian-specific pregnancy recommendations. ANCOVA tests were used to compare mean differences in total GWG across the timing of diagnosis. The timing of GDM diagnosis and excessive GWG was further evaluated using linear and logistic regression analysis. <b>Results:</b> Among the 4694 women with GDM (mean age 31.7 ± 6.3 years; mean pre-pregnancy BMI 30.4 ± 6.5 kg/m², with 47.6% classified with obesity), those diagnosed in the first trimester (<i>n</i> = 1315) gained 2.29 kg less (95% CI: -2.87 to -1.71 kg) total GWG compared to the third trimester, adjusting for risk factors including pregestational weight. First-trimester GDM diagnosis was associated with 22% lower odds of experiencing excessive GWG (Odds Ratio [OR] = 0.78; 95% CI: 0.72-0.86), compared to the third trimester. Diagnoses before 20 weeks and before 24 weeks had 18% (OR = 0.82; 95% CI: 0.77-0.88) and 19% (OR = 0.81; 95% CI: 0.76-0.87) lower odds of excessive GWG. <b>Conclusions:</b> Early diagnosis of GDM, particularly during the first trimester, is associated with reduced GWG. Integrating earlier GDM screening into routine prenatal care could mitigate excessive GWG.