As artefact-free recordings of the fetal brain bioelectric potentials can only be obtained by specially designed electrodes, an electrode for taking electroencephalogram (EEG) and cardiotocogram (CTG), according to the principle of vacuum electrode developed by Rosen and Scibetta, has been designed. The polygraphic technique was used to examine a total of 65 deliveries, divided into two groups. The first group (n = 33) consisted of newborns free of any signs of hypoxia and acidosis, whereas the second group (n = 32) was comprised of newborns with evident clinical and biochemical signs of hypoxia and acidosis. Fetal hypoxia and acidosis were observed to entail some characteristic changes in EEG, that is, a decrease in the frequency and wave amplitude through the appearance of the isoelectric line (ISO) featuring in severe cases of fetal hypoxia and acidosis. The following changes were found to occur during the development of hypoxia and acidosis:hypoxia, a decrease in the EEG frequency and amplitude, preacidosis with the appearance of both early and late decelerations coupled with a significant drop in the oscillation and, eventually, severe variable decelerations accompanied by terminal bradycardia. The time interval between the manifestation of initial signs of a decreasing central nervous system (CNS) activity and changes in the fetal heart rate was found to be about 10 minutes.