Segmentary fetal branch pulmonary artery blood flow velocimetry: in utero Doppler study.

OBJECTIVE: To evaluate changes in human, fetal segmentary, pulmonary artery blood flow velocimetry throughout pregnancy. DESIGN: Ninety-nine women with a singleton, low-risk gestation between 14 and 37 weeks of pregnancy were selected to participate in a prospective, cross-sectional study. All fetuses were evaluated using power and color Doppler ultrasound. Flow velocity waveforms at three sites of the right pulmonary artery were obtained. The pulsatility index (PI) was calculated in the proximal, mid and distal segment of the pulmonary artery. Mean values and 95% confidence interval (CI) for each segment were determined in correlation with gestational age. RESULTS: A full study that included Doppler measurements of all three segments of the pulmonary artery was completed on 99 fetuses. The highest mean PI of 2.36 was obtained in the proximal segment of the right pulmonary artery (CI = 2.29-2.42), whereas in the mid and distal segments the mean PI decreased significantly to 1.57 (CI = 1.53-1.61) and 1.02 (CI = 1.0-1.0) (P < 0.001), respectively. Throughout gestation, the mean PI measurements in the proximal, middle and distal segments of the branch pulmonary artery increased slightly, but without statistical significance (r = 0.274, 0.248, 0.047), respectively; (P > 0.5). CONCLUSIONS: The data obtained suggests that pulmonary circulation maintains stable vascular resistance during gestation in the human fetus. However, the PI obtained from the separate segments of the branch pulmonary artery is unique and each differs from the other, reflecting the proximity to the heart and the peripheral impedance at each location.