Measurements of the Dimensions and Doppler Flow Velocities of the Aorta, Main Pulmonary Artery, Ductus Arteriosus, and Branch Pulmonary Artery in the Normal Human Fetus-a Preliminary Study on the Flow Distribution-

In order to assess the growth and flow distribution of the great arteries and their major branches in the human fetal heart, a prospective fetal echocardiographic study on 127 pregnant women was performed, The vascular dimensions and Doppler average velociues of the aorta, main pulmonary artery, branch pulmonary artery and ductus arteriosus were measured from videotapes. Dimension ratios and average velocity ratios were calculated only when both values for comparison were measured in the same examination. The flow volumes of the aorta and main pulmonary artery were calculated when possible. The measured and calculated values were correlated with the gestational period. The vessel diameters and average velocities in each site increased linearly from gestational period of 15 weeks to 40 weeks. The diameter ratio of the main pulmonary artery to the aorta increased slightly from 1.13 at gestational age of 15 weeks to 1.31 at term. The diameter ratio of the ductus arteriosus to the branch pulmonary artery was 1.28( +- 0.18) and did not change with gestational period. The average velocity ratio between the main pulmonary artery and the aorta was 0.88( +- 0.24) and the ratio between the ductus and branch pulmonary artery was 1.71 (+- 0.54) and these ratios were not significant when compared to fetal growth. The calculated flow volumes of the aorta and the main pulmonary artery increased polynominally with increasing gestation. The flow ratio between the main pulmonary artery and the aorta was about 1.37. The ductal and branch pulmonary arterial flows were not calculated. However the flow ratio between the ductus arteriosus and one branch pulmonary artery was estimated by the product of (diameter ratio)" x (average velocity ratio) between two sites, which was 2.8. In the human fetus, the relative size of aortic and pulmonary pathways and the flow distribution seem to be different from the results obtained from animal studies