ventricles; 7, caval long-axis view; 8, ductal arch view; 9, aortic arch view (From the American Society of Echocardiography Guidelines and Standards for Performance of the Fetal Echocardiogram J Am Soc Echocardiogr 2004;17:803–810.) FIG 8.2 Anatomic correlates for each of the designated tomographic imaging planes used for imaging of the fetal cardiovascular system Each numbered view relates to the clockwise illustration of the fetal heart in Fig 8.1 Ao, Aorta; IVC, inferior vena cava; LA, left atrium; LV, left ventricle; MV, mitral valve; PA, pulmonary artery; PD, patent ductus; RA, right atrium; RV, right ventricle; SVC, superior vena cava (From the American Society of Echocardiography Guidelines and Standards for Performance of the Fetal Echocardiogram J Am Soc Echocardiogr 2004;17:803–810.) Three-Dimensional Imaging Three-dimensional (3D) imaging of the fetal heart has been performed for over 20 years.39 Studies have demonstrated improved diagnostic accuracy of fetal congenital heart disease with the performance of 3D ultrasound compared with two-dimensional (2D) imaging techniques alone.40,41 In addition, 3D ultrasound allows for better visualization of complex spatial relationships, which may be particularly helpful when counseling parents regarding potential postnatal surgical strategies for their unborn child.42 Color Doppler Color Doppler interrogation adds tremendous value to the assessment of fetal cardiovascular well-being by establishing the degree of valvar stenosis and regurgitation, if present Mild tricuspid regurgitation may be seen throughout gestation and is frequently a benign finding,43,44 but tricuspid regurgitation detected during early scanning, from 11 to 14 weeks, may be a marker for aneuploidy even in the absence of structural heart disease.45 In contrast, regurgitation across the mitral, pulmonic, or aortic valves is usually not a normal finding and suggests pathology secondary to underlying structural cardiac disease or fetal cardiac failure Cardiovascular physiology can also be assessed by color Doppler echocardiography by determining the direction of blood flow In the normal fetal circulation, the direction of shunting is right to left at both the patent foramen ovale and the arterial duct Abnormal directions of flow at these sites may suggest cardiac disease For example, left-to-right flow at the patent foramen ovale or bidirectional shunting through the arterial duct with reversal of flow in the transverse aortic arch may indicate inadequacy of the left ventricle.46,47