PEAK VELOCITY OF THE OUTFLOW TRACT OF THE AORTA - CORRELATIONS WITH ACID-BASE STATUS AND OXYGENATION OF THE GROWTH-RETARDED FETUS

Objective: To correlate the peak velocities of the aortic outflow trac t of growth-retarded fetuses with fetal acid base status and oxygenati on measured in utero. Methods: Thirty-one growth-retarded fetuses with abnormal umbilical pulsatility index (PI) measurements underwent feta l blood sampling. Blood pH, carbon dioxide pressure (PCO2), oxygen pre ssure (PO2), oxygen saturation, lactate concentration, and hemoglobin concentration were measured. Using color Doppler equipment, we measure d the peak velocities of the outflow tract of the aorta, pulmonary art ery, and ductus arteriosus before fetal blood sampling. Results: The p eak velocities measured in the outflow tract of the aorta, pulmonary a rtery, and ductus were significantly lower in growth-retarded fetuses than in 140 normal fetuses of comparable weight. The correlation obser ved between pulmonic and aortic peak velocities was significant (r = 0 .84), as was that between pulmonic and ductal peak velocitied (r = 0.7 4). Growth-retarded fetuses with abnormal aortic peak velocities had s ignificantly lower values of pO(2), oxygen content and pH, and had hig her lactate concentration and PCO2 than did growth-retarded fetuses wi th normal peak velocities. Estimated fetal weight and umbilical PI (me an +/- standard deviation) were not significantly different in these t wo groups. Moreover, significant direct correlations were found betwee n proximal aortic peak velocities and lactate concentrations (correlat ion coefficient 0.71, P <.0001) and O-2 content (P <.02, r = 0.42). Co nclusion: For growth-retarded fetuses, Doppler peak velocity in these vessels is significantly lower than in normal fetuses of comparable we ight. Aortic, pulmonic, and ductal peak velocity correlated significan tly. Growth-retarded fetuses with abnormally low peak velocity in the outflow tract of the aorta have a higher risk of acidemia and hypoxia than those with normal velocities.