Human fetal cerebral circulation - Perinatal Doppler velocimetry and fetal pulse oximetry studies

The studies upon which this thesis is based were designed to evaluate normal fetal and neonatal adaptation and the effects of obstetrical interventions during labor and delivery on fetal and neonatal cerebral circulation. Non-invasive Doppler ultrasound was used to record blood flow velocities from the middle cerebral artery (MCA) both antenatally from the fetus, and from the newborn in the early neonatal period. Moreover, a new method of fetal surveillance, fetal pulse oximetry, was assessed in a methodological study, and in a pilot study during maternal hyperoxygenation.

Neither vibroacoustic stimulation nor uterine contractions during the first stage of labor caused any changes in pulsatility index (PI) of the fetal MCA. Using a close fitting face mask with a reservoir, PI significantly increased during maternal hyperoxygenation and mean fetal oxygen saturation, recorded by pulse oximetry, increased by 12 %. Three minutes after oxygenation had stopped, fetal values returned to the pre-oxygenation level. Significant changes in PI occurred immediately after delivery. Compression and decompression of fetal head at the moment of birth might contribute to these changes. During the first hour postpartum there was a significant increase in PI, major determinants of which were changes in partial pressure of oxygen and carbon dioxide. Comparing babies delivered by elective cesarean section (c.s.) versus vaginally delivered babies a significantly higher PI value was found at 1 hour in the c.s. group after delivery; no differences were found 24 hours after delivery.

A new method of fetal surveillance in labor, fetal pulse oximetry, was evaluated. Of 96 oxisensors, 91 (95 %) were successfully placed and displayed the fetal arterial oxygen saturation (SpO2). In two thirds of the recordings acceptable signals of SpO2 were obtained. A significant fall in mean SpO2 was found between the first and the second stages of labor. No serious adverse effects of the sensor were noted. Further research is needed to evaluate the possible clinical value of the method.