Pregnancy - What Is an Ultrasound Test?

There are a variety of tests that an expectant mother can have performed to gain information about the health of her growing fetus. Some, like amniocentesis, have been around for over 100 years. Ultrasound was introduced in the 1960s, though early tests had limited value. Modern tests are much clearer, some even in 3-D, many showing motion.

Today, ultrasound is clear, simple, and (as medical tests go) relatively inexpensive. Most are covered by standard insurance plans that cover pregnancy.

Also called sonography or just 'a scan', the woman's abdominal area is exposed to harmless ultra-high frequency sound waves. The echoes are then recorded and interpreted by a computer program - then projected onto a screen. The basic principle is similar to that used in fishing boats, submarines and other applications.

Unlike X-rays they produce no ionizing radiation, though the sound waves still carry energy. Nevertheless, the procedure is safe and painless. It has the added advantage that it can examine soft tissues that don't show up as clearly in x-rays, and the images are displayed in real-time. Since there are no ill-effects produced by the test, it can be repeated as often as desired as the fetus develops.

The technician (often your physician) uses a small, hand-held wand that travels over the surface of the skin. A clear gel is applied to the skin beforehand to eliminate air between the wand and the surface, producing improved results. Unlike amniocentesis and other tests, it's non-invasive and the preliminary results are available immediately. It takes no more than half an hour.

More extensive analysis of the results can be performed by a trained specialist, if desired. A report is typically sent to your physician. From the results, doctors can detect physical abnormalities, tissue rupture, bleeding or simply whether problem implantation has occurred.

But apart from detecting potential problems, the test is used to provide useful information. It can reveal sex and age and record at the development process. It can also show the physical location of the baby within the womb. That helps determine if a breech birth is likely and other potential positioning issues. With that advanced look, delivery can be better planned.

The procedure has limitations, however. Ultrasound waves, unlike regular sound waves, don't travel as efficiently through air. As a result, any areas where air pockets exist - such as the stomach itself - won't yield as much information. Also, they don't penetrate bone as well as x-rays and the waves are dampened as they pass through fatty tissue. The results may be less useful for obese women.

Those limitations can be overcome by supplementing ultrasound with other tests, such as amniocentesis and others that use chemical indicators to give useful data about the baby's health.

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