Peak velocity of the outflow tract of the aorta : correlations with acid-based status and oxigenation of the growth-retarded fetus

Objective: To correlate the peak velocities of the aortic outflow tract of growth-retarded fetuses with fetal acid base status and oxygenation measured in utero. Methods: Thirty-one growth-retarded fetuses with abnormal umbilical pulsatility index (PI) measurements underwent fetal blood sampling. Blood pH, carbon dioxide pressure (PCO2), oxygen pressure (PO2), oxygen saturation, lactate concentration, and hemoglobin concentration were measured. Using color Doppler equipment, we measured the peak velocities of the outflow tract of the aorta, pulmonary artery, and ductus arteriosus before fetal blood sampling. Results: The peak velocities measured in the outflow tract of the aorta, pulmonary artery, and ductus were significantly lower in growth-retarded fetuses than in 140 normal fetuses of comparable weight. The correlation observed between pulmonic and aortic peak velocities was significant (r = 0.84), as was that between pulmonic and ductal peak velocities (r = 0.74). Growth-retarded fetuses with abnormal aortic peak velocities had significantly lower values of PO2, oxygen content and pH, and had higher lactate concentration and PCO2 than did growth-retarded fetuses with normal peak velocities. Estimated fetal weight and umbilical PI (mean ± standard deviation) were not significantly different in these two groups. Moreover, significant direct correlations were found between proximal aortic peak velocities and lactate concentrations (correlation coefficient 0.71, P <.0001) and O2 content (P <.02, r = 0.42). Conclusion: For growth-retarded fetuses, Doppler peak velocity in these vessels is significantly lower than in normal fetuses of comparable weight. Aortic, pulmonic, and ductal peak velocity correlated significantly. 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.