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 velocity waveforms from fetal middle and distal arterial pulmonary branches in the second half of normal pregnancy and to determine repeatability and inter-relationship of flow velocity waveform recordings from proximal, middle 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 time-intervals in 25 separate normal pregnancies. Results: Acceptable repeatability of flow velocity waveforms from fetal arterial pulmonary branches was established with coefficients of variation below 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 ratio and pulsatility index. The distal arterial pulmonary branch displayed a monophasic 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 index. Significant inter-pulmonary changes were found for all pulmonary arterial waveform parameters. Conclusions: Alteration in pulmonary vascular resistance may play a role in gestational age-related changes, whereas changes in vessel branching/diameter and in the distance between the heart and more distal arterial pulmonary vessels may cause inter-pulmonary differences.