What is an ultrasound?

An ultrasound (sometimes called a sonogram) is a noninvasive diagnostic test that uses sound waves to create images of internal organs. During your pregnancy, the ultrasound technician will use ultrasound technology to see your baby and gather valuable information about his health. During the exam, the sonographer transmits high frequency sound waves through your uterus that bounce off your baby. A computer then translates the echoing sounds into video images that reveal your baby's shape, position, and movements. The series of television-monitor images is called a sonogram. The words ultrasound and sonogram are often used interchangeably. (Ultrasound waves are also used in the handheld instrument called a Doppler that your practitioner uses during your prenatal visits to hear your baby's heartbeat.)

You may have a standard ultrasound between 16 and 20 weeks, or you may have one as early as 4 or 5 weeks or any time after that if there are signs of a problem. Most people look forward to it because it gives them a first glimpse of their baby. The technician will probably present you with a grainy printout of the sonogram as a keepsake.

What's the procedure like?

There are several types of ultrasound examinations. The two most common procedures are transvaginal scan; specifically designed transducers are used inside the vagina to generate ultrasound images. Most often used during the early stages of pregnancy, access cervical length and diagnose low lying placenta.

Standard Ultrasound is the traditional exam which uses a transducer over the abdomen to generate 2-D images of the developing fetus.

The sonographer will slide a transducer (which looks a little bit like a telephone receiver) back and forth over your stomach to transmit the sound waves. As a computer translates the resulting echoes into pictures on a television monitor, your baby will appear on the screen before your eyes. During the scan, the sonographer takes the baby's measurements and takes still pictures of the baby's anatomy and everything else she needs to document in her report for your doctor. While you may be anxious to know what she's seeing, you may need to wait until your practitioner has seen the results and can discuss them with you.

A basic ultrasound takes about 15 to 20 minutes. A more detailed (level II) scan, which may use more sophisticated equipment, can take anywhere from 30 minutes to 90 minutes or more.

What if the ultrasound shows a problem?

Don't panic. Often, a follow-up test shows that a suspicious ultrasound is no cause for concern. But in the unlikely event that your baby has a health problem, the information from the ultrasound can help your practitioner determine how to give your baby the best outcome possible. Knowing about other birth defects can help your practitioner decide how to deliver the baby safely and to prepare to care for the baby right after birth. In any case, it's important to consider all the options, whether that means making the difficult decision to terminate a pregnancy, intervening medically, or preparing for the birth of a baby who needs special care. A genetic counselor can be an invaluable resource.