3D ultrasound represents an ultrasonographic method of imaging of a fetus or its structures in a three-dimensional way. The shortcut "3D" stands for "three-dimensional" imaging. The result of the 3D imaging is spacial, but stationary (immovable) image of a fetal structure.
4D ultrasound, unlike 3D ultrasound, represents a real-time three-dimensional imaging. The "fourth D", in the shortcut "4D", is the "time". That's why the 4D ultrasound enables to see real fetal movements or its structures three-dimensionally.
3D/4D ultrasound can be carried out anytime during pregnancy and may be a convenient addition to conventional 2D (two-dimensional) ultrasound. Limiting determinants of the 3D/4D imaging (and in fact this holds good for the 2D ultrasound too) are various factors as patient's abdominal wall thickness, scars in the scanning area, position of the placenta, position of the fetus, lack of the amniotic fluid, etc. Quality of the final imaging is therefore variable in various patients, and in some cases it is even impossible to perform 3D or 4D ultrasound satisfactorily.
3D/4D ultrasound is often used as an effective method of fetal demonstration to the parents, which undoubtedly is an unforgettable emotional experience. But first of all, these modalities are used as a medical diagnostic tool. 3D ultrasound enables to count more precise volumes of various organs or pathological structures. It also allows better visualization of fetal skeleton, to judge some superficial fetal anomalies, e.g. cleft lip, tumors, neural tube defects, etc. (of course, these anomalies can also be seen in classical 2D imaging). Some special 3D/4D imaging techniques, like for example "STIC" (Spatio Temporal Image Correlation), enable detailed representation of cardiac anomalies, and so on
It is important to emphasize the fact, that there is no such fetal anomaly requiring exclusively 3D or 4D ultrasound for its detection, and the classical 2D ultrasound still represents the main diagnostic tool of prenatal ultrasonographic examination.
3D ultrasound - third trimester of pregnancy
Following images demonstrate comparison of prenatal ultrasound images with postnatal appearance of the newborn.
3D ultrasound - second trimester of pregnancy
3D ultrasound - first trimester of pregnancy
Following "funny images" of a 12-weeks-old fetus demonstrate possibilities of work with a volume data set acquired by 3D ultrasound. It is possible to choose any direction of view, demonstrate any imaging plane, or cut away those parts of the volume hindering view of desired structures. Such adjustment of the 3D images can be done offline, directly in the ultrasound machine or in a computer.