Metabolic acidemia may cause cerebral palsy or perinatal death. Its detection is the major goal of perpartum fetal evaluation. Sensitivity of continuous fetal heart rate analysis is excellent, but the lack of specificity of this test can lead to inadequate intervention during labour. Fetal scalp pH is directly reliable to fetal acid-base status. In every situation where fetal heart rate displays ominous pattern, a potential acidemia can be detected with fetal scalp pH analysis. Intervention is recommended in the next 30min when fetal scalp pH is bellow 7.20. Complete analysis of fetal acid-base status parameters, including base excess and lactatemia allows a more precise detection of metabolic acidemia. Described since 1962, the place of fetal scalp pH analysis is still central in our daily practice.