[Disorders of the fetal oxygen supply during labor--retrospect and prospect of diagnostic possibilities].

Uterine blood flow decreases during uterine contractions. Under physiological conditions there is however an uterine hemodynamic buffer mechanism to guarantee a sufficient oxygen supply to the fetus even during uterine contractions. Heart rate decelerations occur therefore not during the period of cervical dilation but in the second stage of labor. In disorders of pregnancy uterine blood flow is primarily reduced and the slightest uterine contraction exhibits signs of fetal hypoxia, i.e. deceleration of fetal heart rate. Heart rate decelerations signify the possibility of the deterioration of the fetal acid base status. But the degree of fetal acidosis can be estimated only by fetal scalp blood sampling. A valuable tool to predict fetal hazard is to measure the transcutaneous PO2. Numerous hypoxic episodes decrease not only the arterial PO2 but also the skin blood flow which demonstrates a reduced peripheral circulation. This, however, is an indication of severe fetal stress in utero.