[Acute and chronic reduction of diastolic blood flow velocity in fetal umbilical arteries: a Doppler ultrasound study]

Abstract

The significance of increased placental resistance for the development of fetal distress was examined in 800 pregnant women by pulsed Doppler flow velocimetry of the umbilical arteries. Moderately elevated resistance with reduced diastolic flow velocities with forward flow throughout the diastole, leads to an increased frequency of cesarean section for fetal distress and to a more negative fetal outcome. Severely elevated resistance of the fetal placental circulation shows absent diastolic velocities or even a diastolic reverse flow in the umbilical arteries. In 90% of 25 pregnancies this flow pattern leads to a premature delivery by cesarean section for fetal distress or to intrauterine fetal death. Standardised conditions of the Doppler signal measurement are required, before an absence of diastolic flow velocities is diagnosed. Acute changes in the resistance of the fetoplacental circulation were measured in 6 fetuses showing variable decelerations of the fetal heart rate (FHR). In 3 fetuses the flow curves showed a rapid change from normal to absent and to reverse diastolic flow during a period of time of 20-25 sec, which can indicate an acute resistance and a mechanical occlusion of the umbilical cord. Nevertheless, we found in 2 fetuses variable decelerations without any changes in the flow pattern of the umbilical arteries except for a frequency effect. One fetus showed both types of flow changes. Since two completely different sorts of flow changes exist, we conclude, that umbilical cord compression is not always the cause of variable decelerations of the FHR.