Three-dimensional Sonography in the Assessment of Normal Fetal Anatomy in Late Pregnancy

More recent technological breakthroughs in diagnostic ultrasound have surpassed all expectations. With these advances, clinicians now have the tools needed to contend with many significant diagnostic challenges. However, these new technologies are so numerous and have been introduced in such rapid succession that considerable confusion surrounds their operation and application. Indeed, with the advent and evolution of threedimensional (3D) ultrasound technology over the last 15 years, we now stand at a new threshold in noninvasive diagnosis. The progression from two to three-dimensions has brought with it a variety of new options for imaging, storing and postprocessing of the ultrasound data. This technology gives ultrasound the multiplanar capabilities that were previously reserved for computed tomography and magnetic resonance imaging. In addition, it can generate surfacerendered and transparent views that provide entirely new diagnostic capabilities. The main advantages of this new technology in obstetrics include improved assessment of the complex anatomic structures, surface-scan analysis of fetal fingers and toes, three-dimensional examination of the fetal skeleton, spatial presentation of blood flow information, and volumetric measurements of the fetal organs. When operating in multiplanar mode, the three-dimensional orientation of tomograms is unlimited, even with limited probe manipulation or inadequate position of the fetal structures. These imaging capabilities are extremely important during the first trimester of pregnancy when manipulations with the vaginal probe are restricted and obtainable ultrasound sections are limited. During the transabdominal scanning, frontal planes parallel to the fetal abdominal wall that are unobtainable with conventional ultrasound became visible. Additional progress has been achieved through the possibility of eliminating surrounding structures. It has to be emphasized that, rather than representing an alternative, the threedimensional technique is complementary to the conventional ultrasound technique in the field of prenatal diagnosis. However, 3D imaging is superior in solving specific diagnostic problems. A comparison of 2D and 3D techniques shows that in a large percentage of cases 3D offers a diagnostic gain owing to the possibility of surfaceand transparent mode imaging. As with any new technique, three-dimensional ultrasound scanning has some limitations. For example, fetal and maternal movements during the scanning process lead to motion artifacts that can degrade the image quality. Fetal surface rendering primarily depends on sufficient amniotic Abstract