Fetal pulmonary venous blood flow velocities in a normal population and new calculated reference values

OBJECTIVE: The aim of this study is to establish new Doppler reference values in a population with normal pulmonary veins during different phases of the fetal cardiac cycle for maximum blood flow velocities during ventricular systole (S), early ventricular diastole (D), atrial contraction (a), intensity-weighted mean velocity (Vmean) and the indices derived from these parameters [(S - a)/D] and [(S - a)/Vmean]. METHODS: The pulsed-wave color advanced dynamic flow Doppler technique was used in a prospective cross-sectional study of 365 low-risk pregnancies between 18 and 41 completed gestational weeks. Reference ranges were calculated for the individual measuring parameters based on a growth function from a four-parameter class of monotonic continuous functions according to the smallest square principle. RESULTS: During the observation period of 18 to 41 gestational weeks, a continuous increase was evident in maximum flow velocities for ventricular systole (S), early ventricular diastole (D), atrial contraction (a) and intensity-weighted mean velocity (Vmean) of 14.7 to 431.1, 12.5 to 426.2, 5.4 to 411.9 and 8.7 to 421.6 cm/s, respectively. Venous indices, however, showed a decrease with increasing gestational age: (S - a)/D from 0.9 to 0.7 and (S - a)/Vmean from 1 to 0.9. CONCLUSION: The newly established normal values for the fetal pulmonary vein can be used in standardized Doppler sonography measurement to assess the left atrial pressure in the fetal heart.