Three-dimensional ultrasonic images of normal fetus

The purpose of this study was to assess the usefulness and feasibility of 3-dimensional (3D) ultrasound for routine fetal observation.

Eighty-five normal pregnancies with gestational ages of 20-36 weeks were studied. A conventional ultrasound scanner with a specially designed operation unit, frame memory, and 3D probe was the apparatus used in this study. The unit has a circuit board consisting of digital integrated circuit chips designed to make calculations of volume ray tracings for volume rendering in real time. For each fetus, scanning was performed with different levels of opacity in the equation for volume rendering. In areas where there was an inadequate amniotic fluid pocket to perform an adequate examination, the pregnant woman was asked to push the fetus to the opposite side by gently pressing on her abdomen.

Face, limbs, and fingers which are difficult to visualize on conventional ultrasonography could be seen clearly. Extremely satisfactory images were obtained at between 24 and 34 weeks of gestation that produced sonographic pictures easily recognized even by laypersons. Beyond 34 weeks of gestation due to the relative decrease in the size of amniotic fluid pockets, and before 24 weeks of gestation due to frequent fetal movement, the soft tissue of fetuses is thin and its acoustic impedance is virtually the same as that of water, so surface-rendered images are less satisfactory. In addition, the anterior wall placenta, multiple pregnancies, and oligohydramnios made viewing even more difficult.

Between 24 and 34 weeks of gestation, 3D ultrasound is a feasible and useful procedure for routine antenatal examination.