OBJECTIVE: Evaluate obstetric characteristics during the last two hours of labor in neonates born with acidemia. DESIGN: Case-control study. SETTING: Delivery units at two university hospitals in Sweden. STUDY POPULATION: Out of 28,486 deliveries during 1994-2004, 305 neonates had an umbilical artery pH value or = 7.05 and an Apgar score > or =7 at 5 minutes. Obstetric characteristics, cardiotocographic patterns and oxytocin treatment during the last two hours of labor were recorded. RESULTS: In the univariate analysis, > or =6 contractions/10 minutes (odds ratio (OR) 4.94, 95% confidence interval (CI) 3.25-7.49), oxytocin use (OR 2.20, 95% CI 1.66-2.92), bearing down > or =45 minutes (OR 1.77, 95% CI 1.31-2.38) and occipito-posterior position (OR 2.18, 95% CI 1.19-3.98) were associated with acidemia at birth. In the multivariate analysis, only > or =6 contractions/10 minutes (OR 5.36, 95% CI 3.32-8.65) and oxytocin use (OR 1.89, 95% CI 1.21-2.97) were associated with acidemia at birth. Among cases with > or =6 contractions/10 minutes, 75% had been treated with oxytocin. Pathological cardiotocographic patterns occurred in 68.8% of cases and in 26.1% of controls (p