Fetal three-dimensional ultrasound: quantitative assessment

Abstract

In this communication, we report our studies on the clinical use of quantitative 3D ultrasound (US) in assessing fetal organ volume and circulation. In brief, our studies can be divided into three phases as follows. Phase I: Fetal organ volumetry. Conventional 2D US has the limitation in assessing fetal organ volume, especially for the fetal organs with unique shapes. In other words, 2D US volumetry has to assume fetal organs have ideal geometric shapes, which is not correct. With the advent of 3D US, fetal organ volumetry can be assessed. We have reported a series of fetal organ volume assessments using 3D US, such as fetal liver, lungs, brain, cerebellum, and renal volumes, and proved that 3D US can achieve high reproducibility and accuracy in assessing fetal organ volumes. With these normal data of 3D fetal organ volumetry, fetal organ growth can be assessed more precisely, and thus abnormal conditions in fetal growth may be revealed. Phase II: Fetal weight prediction. To date, the accuracy of fetal weight prediction by 2D US remains to be improved. Using 3D US in assessing fetal upper arm volume and fetal thigh volume, we obtained better results in predicting fetal weight than using conventional 2D weight-predicting formulae. Other investigators have also confirmed our studies that fetal weight prediction may be improved by using 3D volumetry. Phase III: Vascularization and flow of fetal organs. The vascularization and blood flow of fetal organs cannot be assessed directly by 2D US. With the quantitative 3D power Doppler, the vascularization and flow of fetal organs can be evaluated directly in utero. The quantitative 3D power Doppler flow indexes, i.e., vascularization index (VI), flow index (FI), and vascularization-flow index (VFI), of fetal kidney, liver, brain, and placenta all significantly correlated with gestational age. In fetal growth restriction, abnormal VI, FI, and VFI may be detected. In conclusion, we believe that quantitative 3D US will be of help in assessing fetal well-being, either in organ growth or in fetal hemodynamics. Further studies of quantitative fetal 3D US are warranted.