Objectives: We aimed to establish whether macrosomic fetuses in pregnancies complicated by gestational diabetes (GDM) show different Pulsatility Index (PI) values in umbilical artery (UA) than in non-macrosomic fetuses. Methods: We considered 106 pregnant women with GDM. Doppler recordings of UA-PI were performed at 34–41 weeks and related to neonatal birthweight. Pregnancies were divided in two groups according to birthweight, macrosomic group (>4000 g) and controls (90th centile and 4000 g than in controls (PI = 0.69; 95% CI 0.64–0.74 versus PI = 0.87; 95% CI 0.84–0.90, p 90th centile than in controls (PI = 0.79; 95% CI 0.74–0.84 versus PI = 0.87; 95% CI 0.83–0.90; t = 2.653; p = 0.01). Linear regression analysis revealed a significant correlation between UA-PI and neonatal birthweight and between UA-PI and neonatal birthweight centile. Conclusions: Macrosomic fetuses of pregnancies complicated by GDM show lower values of UA-PI compared with controls. Despite UA-PI results, a variable related to macrosomia its role in the management of these pregnancies remains to be established.