OBJECTIVE This prospective randomized trial compares the effects of a 5% glucose solution or no infusion during labor on glucose levels, pH, pO2, pCO2, and base excess (BE) of normal pregnant women in early labor and at delivery, and on fetal cord blood. METHODS Forty-three women were randomized to glucose infusion and 38 were controls. RESULTS Starting glucose levels were independent from the fasting state. When no glucose supplementation was given, the labor itself was associated with a reduction of mean pH (from 7.42 to 7.36, P = 0.00001), mean pCO2 (from 25.7 to 24.4 mm Hg, P = 0.04), and mean BE (from -6.3 to -9.8 mEq/L, P = 0.00001), and an increase of capillary glucose (from a mean of 83 to 105 mg/dL, P = 0.00001). Infusions of glucose did not significantly alter maternal acid-base balance at delivery. pH, PO2, pCO2, and BE were similar in arterial and venous cord blood of both groups. No variables correlated with cord blood glucose levels or with glucose vein-artery difference. CONCLUSIONS We conclude that a 5% glucose infusion does not significantly reduce maternal acidemia associated with vaginal delivery and therefore its use cannot be recommended, since maternal glucose is largely available during labor. Intrapartum glucose infusions do not alter the acid-base balance, when the fetus is well oxygenated.