Pulmonary venous blood flow in the human fetus

The objective of this study was to assess the feasibility of recording pulmonary venous blood flow in the human fetus, and to evaluate its relationship with gestational age. We studied 152 singleton pregnancies between the 19th and 40th weeks of gestation. One hundred and one cases were studied cross-sectionally to gather data on color flow visualization, and 51 were studied longitudinally. The upper right pulmonary vein was interrogated by pulsed wave Doppler to assess pulmonary venous blood flow. On color Doppler, the upper right pulmonary vein could be imaged in 89.6% of cases in the peri-atrial tract and in 75% of cases within the lung. The upper left pulmonary vein could only be imaged in 8% of cases close to the atrium and in 41% of cases within the lung. Reliable velocity waveforms were obtained in 91% of cases. The mean systolic peak velocity was 22.19 +/- 6.39 cm/s and the mean diastolic peak velocity was 22.1 +/- 6.35 cm/s. Both increased significantly with gestational age. Reversed end-diastolic blood flow was present in 18% of cases, regardless of gestational age and fetal heart rate. Expressed as a percentage of the forward flow velocity time integral, its value was 7.65 +/- 5.2%. Our data seem to confirm the presence of pulsatile pulmonary venous blood flow in the second- and third-trimester fetus. Normative data have been established for the second and third trimesters of pregnancy.