Human fetal pulmonary artery velocimetry: repeatability and normal values with emphasis on middle and distal pulmonary vessels

Objectives To establish the nature and gestational age dependency of flow v elocity waveforms from fetal middle and distal arterial pulmonary branches in the second half of normal pregnancy and to determine repeatability and i nter-relationship of flow, velocity waveform recordings from proximal, midd le and distal arterial pulmonary branches. Design Cross-sectional study. Subjects/methods A total of 111 singleton normal pregnancies between 20 and 40 weeks of gestation were studied using a color-coded Doppler ultrasound system. Pulmonary waveforms were obtained at the level of the fetal cardiac four-chamber view Repeatability was tested from two recordings at 15 min t ime-intervals in 25 separate normal pregnancies. Results Acceptable repeatability of flow velocity waveforms from fetal arte rial pulmonary branches was established with coefficients of variation belo w 15%. The nature of middle arterial pulmonary flow, velocity waveforms was similar to that of proximal waveforms and showed a gestational age-related change for diastolic velocity parameters, peak systolic/peak diastolic rat io and pulsatility inner. The distal arterial pulmonary branch displayed a morophasic forward flow velocity profile throughout the cardiac cycle. All velocity parameters of the distal branch remained unchanged with advancing gestation, with the exception of the pulsatility inner. Significant inter-p ulmonary changes were found for all pulmonary alterial waveform parameters. Conclusions Alteration in pulmonary vascular resistance may play a role in gestational age-related changes, whereas changes in vessel branching/diamet er and in the distance between the heart and more distal arterial pulmonary vessels may cause inter-pulmonary differences.