Real-time spectral analysis of the fetal EEG: A new approach to monitoring sleep states and fetal condition during labor

Adverse perinatal events affecting cerebral functions are a major cause of neonatal mortality, morbidity, and long-term neurologic deficit. Intrapartum fetal EEG, which records fetal brain electrical activity, provides a monitoring modality for evaluating the fetal CNS during labor. In this study, we describe a new approach to such monitoring that is based on real-time spectral analysis of the fetal EEG during labor. Fourteen pregnant women with uncomplicated term pregnancies who went into labor participated in the study. Two suction-cup electrodes were applied to the fetal scalp at the occipitoparietal or parietal region after rupture of membranes. Real-time spectral analysis was used to determine the frequency and amplitude of the fetal EEG signal. The spectral edge frequency (SEF) was calculated as the frequency below which 90% of the power in the power spectrum resides. The average EEG amplitude and the SEF were displayed using the density spectral array technique. Fetal heart rate and intrauterine pressure were also measured. Two fundamental EEG patterns were identified: high-voltage slow activity and low-voltage fast activity. The SEF was found to be an excellent index of cyclic EEG activity. Fetal heart rate demonstrated increased variability and an elevated baseline during low-voltage fast activity, whereas both parameters decreased during high-voltage slow activity. During episodes of variable decelerations in the fetal heart rate, a decrease in the SEF was observed, accompanied by an increased EEG voltage. The results obtained substantiate the presence of sleep cycles in the human fetus. This kind of cortical activity monitoring may enable rapid alertness to cerebral hypoxia and allow for prompt intervention thereby decreasing the risk for birth asphyxia and subsequent brain damage.