Longitudinal quantitation of middle cerebral artery blood flow in normal human fetuses

We attempted to quantify noninvasively blood flow of the middle cerebral artery in human fetuses during five distinct periods.

Twenty normal fetuses had color pulsed Doppler ultrasonography of the middle cerebral artery. A total of 68 studies were successfully done and are reported. The Doppler sample was placed as parallel to the direction of the vessel flow as possible. All waveforms were recorded on a strip chart at a preset speed of 100 mm/sec. Six Doppler waveforms were digitized for the time velocity integral (area under the curve is equal to time velocity integral) and averaged. Middle cerebral blood flow was obtained by multiplying the time velocity integral of the Doppler curve by the cross-sectional area of the vessel. The combined cardiac output was obtained by adding the right and left ventricular outputs, which were obtained by multiplying the time velocity integrals by the area of the corresponding annuli. Analysis of variance for repeated measurements was used to determine significance.

The diameter of the middle cerebral artery, the time velocity integral, and the peak flow velocity of the Doppler waveform increased significantly with advancing gestational age. Blood flow to the middle cerebral artery ranged from 23 ml/min at 19 weeks to 133 ml/min at term. Resistivity index values were not correlated with advancing gestational age. The percent of the cardiac output to one of the two middle cerebral arteries remained constant throughout gestation with a range between 3% and 7%.

(1) Time velocity integral, peak flow velocity, diameter, and blood flow of the middle cerebral artery increased significantly with gestational age; (2) the percent of the total cardiac output to the middle cerebral artery does not significantly change with gestational age.