Middle cerebral artery Doppler flow velocity waveforms.

Doppler flow velocity-time waveforms of the middle cerebral arteries at their origin from the internal carotid arteries were obtained serially on 14 patients to determine the alterations of these waveforms with gestational age. Satisfactory recordings were obtained from all patients. The middle cerebral artery waveforms demonstrated a typically biphasic pattern with continuing forward flow in diastole. The peak systolic to end-diastolic ratio (A/B ratio) showed a progressive and significant decline from 6.89 +/- 1.48 at around 25 weeks to 4.23 +/- 0.67 at term. Elevation of diastolic velocities and diminished A/B ratio in the middle cerebral arteries were noted in four fetuses, in whom severe antepartum compromise was diagnosed. The ratio also appeared to decrease with worsening of fetal condition. Because the fetus compensates for hypoxia by increasing blood flow to the brain, Doppler middle cerebral artery waveforms may permit evaluation of fetal compromise and hypoxia.