For years, physicians have relied on traditional ultrasound tests to learn how far along a woman is in her pregnancy, as well as the size, health, and position of the developing baby. Now, four-dimensional (4D) ultrasound lets women and doctors look at facial features and watch the growing baby move.

The Way Ultrasound Works

An ultrasound scanner (or transducer) sends sound waves through the body. These sound waves bounce back to the scanner and produce an image on a computer screen. Ultrasound is generally safe for the developing baby and mother. A technician applies a gel before placing and moving the transducer over the skin. The transducer may also be inserted into the vagina.

The conventional mode of ultrasound scanning is two-dimensional (2D). In other words, the image is made up of thin slices, and only one slice can be seen at a time. Although such an image is very informative to ultrasound professionals, to the average person, the picture may not look at all like a baby.

With 3D ultrasound, a volume of echoes is taken, stored digitally, and shaded to produce life-like images of the fetus. A 4D ultrasound takes the images produced by 3D ultrasound and adds the element of movement. Now, the life-like pictures can move and the activity of the fetus can be studied.

The ability to obtain clear images and activity will depend on the stage of pregnancy and the position of the fetus during the ultrasound exam.

Benefits of 3D/4D Ultrasound

In 3D and 4D ultrasounds, no preparation is needed. Unlike a traditional ultrasound, patients do not need a full bladder, so there is no discomfort.

Some parts of the fetal anatomy can be seen much more clearly than with 2D ultrasound, especially the face, arms, legs, fingers, and toes. For example, cleft palate is more easily detected with 3D ultrasound. In addition, activities of the fetus can be seen that are not possible with 2D. The fetus can be seen to yawn, smile, cry, swallow, blink, and move fingers with 4D.

Being able to view the developing child’s face may promotes bonding. Women typically go home with a set of photographs and a CD with the moving images.

To doctors, 4D reveals more detail about fetal health and small movement. Just as a pediatrician begins an exam by observing a newborn, doctors assess the fetus from head to toe on screen. Watching him or her shift position and breathe, your doctor can check for problems.

“The most important display is the multiplanar display, which can visually cut through organs or structures in any plane,” says Ilan E. Timor-Tritsch, MD, director of the Obstetrical and Gynecological Ultrasound Unit, New York University School of Medicine. The 3D multiplanar display option on the ultrasound machine lets physicians look inside the fetal brain and its cavities.

Cautions

As with other diagnostic imaging, 4D ultrasounds require a doctor’s order and a medical purpose. The American Institute of Ultrasound in Medicine (AIUM) considers 3D/4D imaging a developing technology that is not a replacement for traditional 2D ultrasound.

There is a strong consumer market for 4D ultrasound—even if it might pose as yet undiscovered risks. Because it has no proven benefit over 2D images, some insurance companies do not cover 4D imaging, even with a doctor's order. Despite theoretical risks and extra costs, some expectant parents may choose to obtain ultrasounds on their baby anyway. Most others choose the old fashioned way: waiting until the baby is born to see what he or she looks like.