Cerebral artery blood flow velocity waveforms in normal and small for dates fetuses

Middle cerebral artery (MCA) blood flow velocity waveforms were recorded by a pulsed Doppler system in normal and small for dates (SFD) fetuses. Eighty four normal growth fetuses and 15 SFD fetuses were studied between the 28th and 40th gestational week. The flow velocity waveforms were analysed to determine the resistance index (RI = peak systolic velocity minus end diastolic velocity/peak systolic velocity). The results obtained were as follows: 1. The mean values of RI in the MCA had a peak of 0.802 +/- 0.049 at 32-33 gestational weeks and decreased gradually to a level of 0.686 +/- 0.087 at 40 gestational weeks. 2. In 8 asymmetrical SFD fetuses, the RI values for the MCA were below the normal range (mean -1.5 SD) in 6 cases and normal in 2 cases. 3. The RI values for MCA in all 7 symmetrical SFD fetuses were in the normal range.