The objective of this study was to describe the normal blood flow velocity waveforms in the main branches of the right and left pulmonary arteries in the human fetus and to establish reference ranges for different Doppler parameters during the second half of pregnancy. Cross-sectional data were collected from 86 healthy human singleton fetuses between 18 and 38 weeks of gestation. With advancing gestation a significant increase (p < 0.001) in the peak systolic velocity, time averaged velocity and time velocity integral was observed. The pulsatility index decreased significantly (p < 0.05) in the same period, suggesting a decrease in the pulmonary arterial vascular resistance. The acceleration time (AT) and the ratio of AT to ejection time (AT/ET), described in postnatal cardiology as having an inverse correlation with mean arterial pressure, increased significantly (p < 0.001). This is possibly the result of decreased pulmonary arterial pressure. The data show that Doppler examination of blood flow in the main stem of both the right and the left pulmonary arteries of the fetus is feasible, and increases insight into the lung perfusion of the human fetus. The observed changes throughout gestation are in accordance with animal experiments showing an increase in perfusion as well as a decrease in the vascular resistance and pressure.

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The objective of this study was to describe blood flow velocity waveforms of fetal peripheral pulmonary arteries in normally grown and growth-retarded fetuses. Doppler studies were performed in 182 normally grown fetuses (gestational age 18-40 weeks) and in 61 growth-retarded fetuses (gestational age 24-36 weeks) that were free from structural and chromosomal abnormalities and whose umbilical and middle cerebral artery Doppler findings suggested uteroplacental insufficiency as the most likely etiology of the growth defect. The pulsatility index was used to quantify the velocity waveforms. Successful recordings were obtained in 90.1% of the normally grown and 93.4% of the growth-retarded fetuses. In normally grown fetuses the pulsatility index values significantly decreased with advancing gestation. In growth-retarded fetuses the pulsatility index values were significantly elevated compared to those of normal fetuses. A significant relationship was observed between the severity of hypoxia and pulsatility index values from the peripheral pulmonary arteries in 29 fetuses in which Doppler recordings were obtained immediately before cordocentesis. In conclusion, these data show that in normal fetuses the Doppler-measured impedance to flow in the peripheral pulmonary circulation decreases with advancing gestation. Impedance to flow in the lungs is elevated in the presence of growth retardation and this increase is related to the severity of fetal hypoxia.

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