All About Ultrasound

Ultrasound can be performed at various times during pregnancy:

First Trimester

8-12 weeks: to estimate the number of weeks of pregnancy
10-13 weeks: to check for a neural tube defect, a birth defect of the brain and spinal cord

Second Trimester

16-20 weeks: to help when amniocentesis is being performed
18-20 weeks: to check the baby's growth and size and to look for major birth defects

Third Trimester

To check the amniotic fluid (is there too much or too little?)
To check the baby's well-being and movement

Who: Most pregnant women. Why: To check the age of the baby, identify a multiple pregnancy (twins or more), check the baby's growth and size, and look for major birth defects. Also used to help diagnose certain pregnancy complications. When: Usually at 18-20 weeks; at other times, as needed. How: Ultrasound uses sound waves to show a picture of the baby on a screen. The health care provider rubs a handheld device, called a transducer, across the woman's belly or inserts a probe into her vagina. The woman feels pressure as the provider moves the transducer, but usually no pain. Risks: Considered safe for the mother and baby when properly used and when medical information about pregnancy is needed. Casual use of ultrasound during pregnancy should be avoided.

A routine ultrasound exam, which takes about 20 minutes, can determine the age of the fetus, identify a multiple pregnancy (twins or more), check fetal growth and size, and look for major birth defects. If birth defects are suspected, your provider will refer you for a more detailed ultrasound examination (a level II exam or a 3-D ultrasound).

Ultrasound also is used to help diagnose certain pregnancy complications, such as the causes of vaginal bleeding, and to check fetal well-being late in pregnancy.

When there is a medical reason for the test, ultrasound can provide valuable information leading to treatment that can improve a woman's chances of having a healthy baby.

Ultrasound is considered safe for the mother and baby when properly used and when medical information about pregnancy is needed. Casual use of ultrasound during pregnancy should be avoided.

Many providers offer an ultrasound to all low-risk women just to check on fetal growth and well-being. But don't be too disappointed if your provider doesn't. Studies suggest that low-risk women who have routine ultrasound exams are no more likely to have healthy babies than low-risk women who don't have the test.

Ultrasound does not detect all birth defects, so it cannot guarantee a healthy baby. And, occasionally, a woman receives a "false positive result"; that is, she is told incorrectly that her baby may have a birth defect. Although follow-up exams usually show the baby is healthy, false alarms are frightening.

New ultrasound equipment shows a three-dimensional still view of the fetus (3-D ultrasound). This technology is now available in some medical centers and doctors' offices. The 3-D ultrasound is almost as detailed as a photograph. It may be used when birth defects are suspected. Some facilities provide 3-D scans, without specific medical reasons. A moving-picture version of this technology is called 4-D ultrasound. The American College of Obstetricians and Gynecologists, the U.S. Food and Drug Administration (FDA), and other experts discourage the use of non-medical ultrasound exams because the individuals conducting them may not have adequate training and may give a woman inaccurate or even harmful information.