Relationship between fetal pulmonary trunk and ductus arteriosus flow velocity waveforms in early normal pregnancy.

To establish the relationship between flow velocity waveform patterns from the fetal pulmonary trunk and ductus arteriosus in normal late first- and second-trimester pregnancies, Doppler ultrasound examinations in these vessels were performed in 133 healthy women between 9 and 25 weeks of gestation. Differentiation between pulmonary and ductal blood flow was possible as from 12 weeks onwards resulting in a study population of 78 women. A linear gestational age-dependent increase in peak systolic velocity was found for both the pulmonary trunk and the ductus arteriosus. Ductal peak systolic velocity rose significantly faster with gestational age than pulmonary peak systolic velocity. This may be determined by differences in morphology and effective lumen between these two vessels.