The Difference Between Levels in Ultrasounds

Ultrasounds use high-frequency sound waves to take a non-invasive look inside the body. One of the most common uses for ultrasound is to check on the condition of a fetus during pregnancy. There are several different types of ultrasounds (sometimes called "levels") that give different kinds of pictures and serve different purposes.

General Screening Ultrasound

• The general screening ultrasound is the most common form of ultrasound. Most pregnant women will have this basic-level screening done between the 18th and 20th week of pregnancy. It forms a picture of the fetus in layers, creating a flat, two-dimensional black-and-white image. This image is then used to check on the development of the baby's brain, limbs and internal organs and to check for growths, cysts and other abnormalities.

Targeted Ultrasound

• A targeted ultrasound, sometimes called a "level two ultrasound," is usually done only if the general screening ultrasound detected some sort of abnormality. The targeted ultrasound works the same way as the general screening ultrasound, but is much more detailed and is designed to focus on a much smaller area. For example, if the general screening detected a possible cyst on the brain, the targeted ultrasound would provide a much closer and more detailed view of the just the brain as opposed to the entire fetus.

3-D Ultrasound

• A 3-D ultrasound is usually an elective ultrasound that is used mostly to give parents a better look at their child before it is born. 3-D ultrasounds focus on just the surface of the fetus to provide a more life-like color image. Proponents of this type of ultrasound say that it helps parents create a bond with their child before birth by letting them see their baby as it will look when it is born rather than a black-and-white cross section.

4-D Ultrasound

• 4-D ultrasound works exactly like 3-D ultrasounds, only in motion. This allows parents to in effect take video of their child before it is born. Because they focus only on the surface of the fetus, there is a window where 4-D and 3-D ultrasound are most effective. According to the Expectant Mother's Guide, between 24 and 34 weeks is the best time for a 4-D ultrasound since the fetus will have enough fat that it will look like it does at birth, but will still be small enough to have room to move.