Objective. Umbilical cord acid–base analysis is fundamental for assessing intrapartum hypoxia. The accuracy of arterial umbilical cord blood lactate, pH and base deficit to reflect a low 5-minute Apgar score and hypoxic ischemic encephalopathy (HIE) stage 2–3 was assessed, and new gestational age-adjusted reference standards were compared with traditional stationary reference values. Design and sample. A total of 13,735 pH-validated routine cord acid–base values from singleton deliveries were tested with stationary and gestational age-adjusted reference values using receiver operating characteristic curves and calculation of area under curve. Setting. University hospital. Main outcome measures. Accuracy of low pH, high base deficit and high lactate, alone or in combination, to imply 5-minute Apgar score < 7 or < 4 or HIE. Results. Gestational age-adjusted values were for all parameters significantly better than crude values to indicate Apgar score < 7. For Apgar score < 4, the differences were not significant. The frequency of HIE was 0.046%, making statistical analyses pointless. Gestational age-adjusted lactate had the overall best accuracy and among combinations; a low age-adjusted pH plus high age-adjusted lactate was slightly better than a low age-adjusted pH plus high age-adjusted base deficit. The sensitivity and positive predictive value were low for all parameters. Conclusions. Lactate in cord arterial blood at birth is at least as good as base deficit to reflect an impaired condition at birth, and best when gestational age-adjusted values are used. Due to methodological confounding involved in calculation of base deficit, lactate may replace base deficit as an acid–base outcome parameter at birth.