Your doctor has requested an obstetric ultrasound examination...although you may have heard about ultrasound before, you may still have some questions. The American Institute of Ultrasound in Medicine (AIUM) - an organization composed of doctors, sonographers, and scientists - has put together this pamphlet to answer some of the most commonly asked questions and explain how ultrasound works.

What Is Ultrasound?
Ultrasound is like ordinary sound except it has a frequency (or pitch) higher than people can hear. Ultrasound is sent into the body from a scanning instrument (transducer) placed on your skin. The sound is reflected off structures inside your body and is analyzed by a computer to make an image of these structures on a monitor, which is similar to a television screen. The moving pictures can be recorded on film or videotape. Diagnostic ultrasound is commonly called sonography or ultrasonography.

Why Do Patients Have an Obstetric Ultrasound Examination?
The most common reason for having an obstetric ultrasound examination is to help your doctor determine when your baby is due or to make sure your baby is growing as it should. Your doctor may also want an ultrasound examination to determine the baby's position or to see if you are carrying more than one baby. With an ultrasound examination, the amount of fluid around your baby can be seen. Ultrasonography also may be used to detect some birth defects.

Are There Any Special Preparations Needed for the Examination?
In most cases, no special preparation is needed for the examination. In some cases, your doctor may recommend an endovaginal ultrasound study, which involves the use of a special transducer in your vagina, to improve visualization of your baby or your cervix. A complete obstetric ultrasound examination usually takes between 30 and 60 minutes.

Who Will Perform the Examination?
In most cases, a specially trained professional called a sonographer will examine you. In some cases, a doctor may also examine you or perform the ultrasound exam itself. In all cases, the pictures are reviewed and read by a doctor.

Will It Hurt?
There is no pain from an ultrasound examination. You may feel some pressure from an endovaginal ultrasound examination in which a probe is inserted in your vagina; the probe is the size of a tampon and is smaller than a speculum. You may choose to insert the probe yourself. The ultrasound examination does not affect your pregnancy.

During the scanning procedure, a gel-like material is put on your abdomen and a transducer is placed on your skin. The gel makes it possible for the ultrasound system to see through your skin into your body. The gel may feel cold and, although the gel wipes off easily and does not usually stain clothing, it is a good idea to wear clothes that can be washed.

Can I See My Baby Move?
Your baby's heartbeat and movement of his or her body, arms, and legs can be seen using ultrasound, depending on the age of the baby. Your baby can be seen moving during an ultrasound examination many weeks before you can feel movement.

Will I Learn the Sex of My Baby?
Sometimes it is possible to see the sex of the baby and sometimes it is not. If your baby is lying in an inconvenient position, the baby's sex cannot be determined.

Does an Ultrasound Examination Guarantee a Normal Baby?
No, an ultrasound examination does not guarantee a normal baby. The ability to detect fetal abnormalities depends on many things. For instance, the size and position of your baby may not allow certain abnormalities to be seen. Some types of abnormalities cannot be seen because they are too small or not visible by ultrasound.

Will I Need More Than One Ultrasound Examination?
In many cases, women need only one ultrasound examination or "scan," but for a variety of reasons, your doctor may order additional scans during your pregnancy.

What Is Doppler Ultrasound?
Doppler ultrasound is a special form of ultrasound. This type of ultrasound is useful in evaluating blood flow to the pelvic organs and fetal vessels. The doctor or sonographer performing the scan can display this information in several ways. An audible sound may be used, or the blood flow may be shown as a graphic or color display. It is not painful. The decision to use Doppler ultrasound is often not made by the doctor until the time of the exam; for example, for further evaluation of the heart of the fetus. It is not considered harmful to the fetus.

Is Ultrasound Safe?
The AIUM has a Bioeffects Committee that meets regularly to consider safety issues and evaluate reports dealing with bioeffects and the safety of ultrasound. The AIUM has adopted the following official statement: "There are no known harmful effects associated with the medical use of sonography. Widespread clinical use of diagnostic ultrasound for many years has not revealed any harmful effects. Studies in humans have revealed no direct link between the use of diagnostic ultrasound and any adverse outcome. Although the possibility exists that biological effects may be identified in the future, current information indicates that the benefits to patients far outweigh the risks, if any."