Background/Objectives: The safety of specific parenteral glucose intake values within the range currently recommended by international guidelines for the early acute phase in preterm neonates has not been established. This study aimed to evaluate whether exceeding a data-driven parenteral dextrose intake threshold during the first week of life is independently associated with hyperglycemia, hypertriglyceridemia, metabolic acidosis, and extrauterine growth restriction (EUGR). Methods: This was a single-center retrospective study involving preterm neonates (gestational age ≤ 34 weeks and/or birth weight ≤ 1500 g) admitted to the Neonatal Intensive Care Unit of Policlinico Umberto I, Rome, between 2015 and 2022. The analysis followed two pre-specified steps: (1) data-driven identification of an exposure threshold by restricted cubic spline logistic regression; (2) multivariable analyses with the dichotomized exposure, adjusting for gestational age, birth weight, enteral nutrition timing, neonatal morbidity, and perinatal compromise. Results: 389 preterm neonates met eligibility. The data-driven inflection point of the spline-derived log-odds curve identified a threshold of 7 g/kg/day. Exceeding this threshold during the first week of life was independently associated with both hyperglycemia (adjusted odds ratio 5.55, 95% confidence interval 2.56 to 12.03; p < 0.001) and hypertriglyceridemia (adjusted odds ratio 4.36, 95% confidence interval 1.41 to 13.45; p = 0.010), but not with metabolic acidosis or with EUGR at 36 weeks postmenstrual age. The divergence in daily parenteral glucose intake between cases and controls was apparent from the second day of life. Conclusions: Exceeding 7 g/kg/day of parenteral dextrose was independently associated with early metabolic complications, but not with growth outcomes. A safety threshold for parenteral glucose may exist within the currently recommended intake range; prospective multicenter studies are needed before clinical recommendations can be drawn.