Objective To evaluate the effectiveness of using hospital-based 40% dextrose gel (DG) in preventing and treating asymptomatic hypoglycemia in infants of diabetic mothers (IDM), large for gestational age (LGA), and macrosomic neonates. Methods A medical chart review was conducted to compare data between before (April 2018 to March 2019, epoch 1) and after (September 2020 to November 2021, epoch 2) 40% DG implementation. DG, prepared by the hospital pharmaceutical unit, was applied within 30–45 min after birth, and three additional doses could be repeated during the first 6 h of life in combination with early feeding. The primary outcome was the rate of intravenous dextrose administration. Secondary outcomes were the incidence of hypoglycemia, first capillary blood glucose concentrations, and the length of hospital stay. Results Six hundred forty-three at-risk newborns were included (320 before and 323 after implementation of DG). Maternal and neonatal baseline characteristics were not different between the two epochs. The incidence of hypoglycemia was not different (17.8% in before versus 14.6% in after implementation, p = 0.26). The rate of intravenous dextrose administration after DG implementation was significantly lower than that before DG implementation (3.4% versus 10.3%, p < 0.001, risk reduction ratio = 0.33, 95% CI = 0.17–0.64). The length of hospital stay was not different between the two epochs. Conclusions Implementing a protocol for administration of hospital-based 40% DG can reduce the need of intravenous dextrose administration among IDM, LGA and macrosomic neonates.