Middle cerebral artery flow velocity waveforms in normal and small-for-gestational-age fetuses.

The middle cerebral artery flow velocity waveforms were obtained in 16 normal fetuses in a longitudinal study and in 128 normal fetuses in a cross-sectional study with pulsed Doppler ultrasonography. The pulsatility index values of the middle cerebral artery were higher at 25 to 30 weeks' gestation than those observed during the two periods of major cerebral cellular multiplication in the human fetus. In 9 of the 16 fetuses studied longitudinally we compared the pulsatility index values obtained at the end of gestation with those obtained at 1 month after delivery; no significant difference was observed. The pulsatility index of the middle cerebral artery was also determined in 33 small-for-gestational-age fetuses. A middle cerebral artery pulsatility index value below our normal range was recorded in 9 of the 33 small-for-gestational-age fetuses (27.3%). These small-for-gestational-age fetuses with abnormal pulsatility index values had a significantly higher incidence of abnormal fetal heart rate and admission into the neonatal intensive care unit. There were three deaths in the nine small-for-gestational-age fetuses with abnormal pulsatility index values (33.3%) and three deaths in the 24 small-for-gestational-age fetuses with normal pulsatility index values (12.5%). Our data indicate that the pulsatility index of the middle cerebral artery in the normal human fetus has a parabolic pattern during pregnancy and does not change significantly after delivery. The results suggest that the small-for-gestational-age fetus with a normal middle cerebral artery pulsatility index is at lower risk than the fetus with abnormal pulsatility index values; moreover, management of the small-for-gestational-age fetus may be aided by the study of the middle cerebral artery waveforms.