Objectives To describe the nature of flow velocity waveforms from fetal mid
dle and distal venous pulmonary branches in the second half of normal pregn
ancy in relation to gestation, and to test repeatability and interrelations
hips of flow velocity waveform recordings from proximal, middle and distal
venous pulmonary branches.
Design Cross-sectional study.
Subjects/methods A total of 111 normal singleton pregnancies between 20 and
40 weeks' gestation were studied using a color-coded Doppler ultrasound sy
stem. Pulmonary waveforms were obtained at the level of the fetal cardiac f
our-chamber view. Repeatability was tested from two recordings at 15-min ti
me intervals in 25 separate normal pregnancies.
Results The nature of middle and distal venous pulmonary flow velocity wave
forms was comparable with that of proximal waveforms. Acceptable repeatabil
ity of pulmonary venous flow velocity waveforms with coefficients of variat
ion below 15% was established for nearly all velocity parameters and their
ratios. A gestational age-dependent change was found for all flow velocity
waveform parameters including pulsatility index for veins at both middle an
d distal venous levels. Significant inter-pulmonary changes were observed f
or nearly all pulmonary venous waveform parameters.
Conclusions It is speculated that increase in volume flow and venous pulmon
ary pressure gradient plays a role in gestational age-dependent changes, wh
ereas changes in vessel diameter and distance between the heart and more di
stal venous pulmonary vessels are responsible for inter-pulmonary changes.