Doppler echocardiographic studies of diastolic function in the human fetal heart: Changes during gestation

With the combined use of two-dimensional ultrasound and Doppler echocardiography, noninvasive examination of the human fetal heart and circulation has recently become possible. These techniques were employed to investigate diastolic atrioventricular valve flow in the fetal heart in 120 fetuses studied between 17 and 42 weeks of gestation. Two-dimensional ultrasound was used to examine fetal and intrauterine anatomy, and estimates of gestational age were made based on biparietal diameters and femur lengths. Doppler echocardiography was performed with a 3.5 or 5 MHz Doppler sector scanner. Flow velocity patterns were obtained through the tricuspid and mitral valves during diastole. Peak flow velocity during late diastole or atrial contraction (A) was compared with peak flow velocity during early diastole (E) in four groups of fetuses: Group 1,17 to 24 weeks of gestation; Group 2, 25 to 30 weeks; Group 3, 31 to 36 weeks; and Group 4, 37 to 42 weeks. The ratio of A to E decreased significantly as gestational age advanced, from 1.56 ± 0.06 (± SE) to 1.22 ± 0.03 across the tricuspid valve (p < 0.001) and from 1.55 ± 0.04 to 1.22 ± 0.06 across the mitral valve (p < 0.001). In tricuspid valve measurements, peak flow velocity during early diastole increased from 26.3 ± 2.0 cm/s in Group 1 to 36.5 ± 1.7 cm/s in Group 4 (p < 0.001), whereas peak flow velocity during atrial contraction did not change. Mitral valve peak flow velocity during early diastole did not change significantly, whereas peak flow velocity during atrial contraction decreased from 45.8 ± 1.3 cm/s in Group 2 to 34.5 ± 2.7 cm/s in Group 4 (p < 0.001). Tricuspid flow velocities during early diastole and late diastole were greater than mitral flow velocities in 91 fetuses in which both valves were studied (p < 0.0001), thereby providing further evidence of right heart dominance in the human fetus. Diastolic flow into the left and right ventricles in human fetuses is shifted into late diastole when compared with newborns or adults. Doppler echocardiography is a useful technique for the study of human fetal cardiovascular function.