Fetal descending aortic flow in normal and in utero growth-restricted human fetuses

Objective: To determine the hemodynamic and volume blood flow through the descending aorta, just below the ductus, in normally grown fetuses and in growth-retarded fetuses. Methods: One hundred twenty-four two-dimensional directed pulsed Doppler flow studies of the descending aorta were evaluated in 52 normally grown fetuses and 72 growth-restricted fetuses. The maximum diameter of the thoracic aorta was obtained during systole using high resolution ultrasound. Descending aorta peak systolic velocity, time velocity integral, and acceleration time/ejection time were obtained using pulsed Doppler. Six consecutive cardiac cycles were digitized and averaged. The systolic to diastolic ratio of the umbilical artery as obtained at the level of the placental insertion. The descending aorta cross-sectional area was derived and multiplied by the time velocity integral to estimate the volume blood flow through the descending aorta. Results: The diameter of the descending aorta was significantly smaller in a group of growth-restricted fetuses. Time velocity integral, peak systolic velocity, and acceleration time/ejection time and volume blood flow of the descending aorta indexed to estimated fetal weights were not different between the two groups even when the data were reanalyzed based on a systolic/diastolic ratio-greater than 3. Conclusions: The diameter of the descending aorta of growth-restricted fetuses was smaller than the normally grown fetuses. The measured and derived descending aorta hemodynamic parameters were not significantly decreased in growth-restricted fetuses. Aortic flow may thus be quite variable in growth-restricted but not severely compromised fetuses.