From the research work of Lemtis (4) and Kunzel (3) we know that uterine blood f low ( U B F ) decreases fo l lowing vena caval occlusion (VCO) when the mean arterial blood pressure (BP) decreases and/or the venous pressure increases. Fetal heart rate (FHR) wi l l drop when the UBF fal ls below a certain critical level and this decrease in FHR is associated with a . f a l l in Po2 and oxygen Saturation which in i t ia l ly provokes a pressor response in the fetus. Un t i l recently i t has only been possible to consider such pathophysiological questions in animal models, but wi th the development of the tcPo2-technique (1 ) one is now able to investigate this phenomenon in human labour.