LONGITUDINAL QUANTITATION OF MIDDLE CEREBRAL-ARTERY BLOOD-FLOW IN NORMAL HUMAN FETUSES

OBJECTIVES: We attempted to quantify noninvasively blood flow of the m iddle cerebral artery in human fetuses during five distinct periods. S TUDY DESIGN: Twenty normal fetuses had color pulsed Doppler ultrasonog raphy of the middle cerebral artery. A total of 68 studies were succes sfully done and are reported. The Doppler sample was placed as paralle l 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 t he curve is equal to time velocity integral) and averaged. Middle cere bral blood flow was obtained by multiplying the time velocity integral of the Doppler curve by the cross-sectional area of the vessel. The c ombined cardiac output was obtained by adding the right and left ventr icular outputs, which were obtained by multiplying the time velocity i ntegrals by the area of the corresponding annuli. Analysis of variance for repeated measurements was used to determine significance. RESULTS : The diameter of the middle cerebral artery, the time velocity integr al, and the peak flow velocity of the Doppler waveform increased signi ficantly with advancing gestational age. Blood flow to the middle cere bral artery ranged from 23 ml/min at 19 weeks to 133 ml/min at term. R esistivity index values were not correlated with advancing gestational age. The percent of the cardiac output to one of the two middle cereb ral arteries remained constant throughout gestation with a range betwe en 3% and 7%. CONCLUSIONS: (1) Time velocity integral, peak flow veloc ity, diameter, and blood flow of the middle cerebral artery increased significantly with gestational age; (2) the percent of the total cardi ac output to the middle cerebral artery does not significantly change with gestational age.