What is Ultrasound? 

Ultrasound is energy in the form of sound waves.  The sound waves move at a frequency too high to be heard by the human ear.  By reflecting off internal organs and being "read" by scanners, the sound waves create pictures of the internal organs and, during pregnancy, the fetus.  Ultrasound differs from X-rays in that it uses sound instead of X-rays, making it safer for the fetus as well as the mother. 

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How Ultrasound Works 

The type of ultrasound that is most often used, called real-time, combines still pictures in rapid succession to show movement, similar to the frames that make a motion picture.  Real-time ultrasound can show the fetal heartbeat, movements of the arms and legs, and other types of body movements.  The creation of these pictures by ultrasound can show the growing fetus, the number of fetuses in the uterus, and the position of the fetus and placenta.

Another form of ultrasound, called Doppler ultrasound, gives audible signals.  When the sound waves are reflected, they are converted into electrical signals of the fetal heartbeat.  These signals are amplified so they can be heard by the mother and the health care provider. 

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Ways Ultrasound Is Used During Pregnancy 

Ultrasound is not necessary for every woman or in every pregnancy. Your health care provider will discuss with you whether ultrasound will be used and how often it should be done to best suit the health and well-being of you and your baby.  Ultrasound is often used by the health care provider, along with information from your medical background and physical exams, to detect a problem or to monitor a condition.  It can provide information that cannot be obtained with other methods.  In almost all cases, ultrasound will be used with other exams and tests needed to diagnose and treat a problem.  Exams may need to be repeated to monitor a condition or to follow different stages of pregnancy. 

 
Ultrasound is used to examine the growing fetus inside the mother's uterus.  Being able to evaluate the pregnancy in this way is especially important if the health care provider suspects that the fetus is growing improperly or may have an abnormality.  The health care provider can then better help you to reduce the risks to you and your baby. 
In a way, ultrasound serves as a type of physical exam of a fetus.  It can provide valuable information about the fetus's health and well-being, for example: 

. Age of the fetus  
. Whether the size of the fetus is right for its age 
. Rate of growth 
. Location of the placenta 
. Fetal position, movement, breathing, and heart rate 
. Amount of amniotic fluid in the uterus 
. Number of fetuses 
. Detection of some types of birth defects 

A more detailed ultrasound exam may be used to diagnose defects of the fetal head, spine, chest, and limbs, as well as some heart defects.  Ultrasound may also be used along with other special tests to detect problems. 

Doppler ultrasound is used in pregnancy to monitor the fetal heart rate before or during labor.  The fetal heartbeat can indicate the well-being of the baby.  Doppler ultrasound is also used to measure the flow of blood within vessels of the uterus, fetus, and umbilical cord, which connects the fetus and the placenta. 

Sometimes vaginal ultrasound is used during pregnancy to find the cause of bleeding or pain, to diagnose an ectopic pregnancy (in which the fertilized egg has begun to grow in a place other than inside the uterus, such as in a fallopian tube), or to find certain types of birth defects in the fetus early in pregnancy. 

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The Exam 

To prepare for an ultrasound exam, wear comfortable clothes.  In some cases you may be asked to wear a hospital gown.  If vaginal ultrasound is to be used, you may be asked to remove your clothes from the waist down and just be covered with a sheet. 

A full bladder may be needed for some exams.  This will require drinking several glasses of water 1 hour before the exam and not urinating until after the procedure.  A full bladder helps to locate and view the pelvic organs.  Usually the only discomfort patients feel is that of a full bladder. 

For most ultrasound exams, the patient lies on the table with her abdomen exposed from the lower part of the ribs to the hips.  A liquid gel is applied to the surface of the abdomen to improve contact of the transducer with the skin surface.  The transducer is then moved along the abdomen.  The sound waves sent out from the transducer enter the body and are reflected back when they come into contact with the organs and, during pregnancy, the fetus. 

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Safety, Risks, and Benefits 

Although the effects of ultrasound are still being studied, no harmful effects to either the woman or the fetus have been found in over 20 years of use.  The long-term risks of ultrasound, if any, are unknown, but there are many benefits.  It does not involve harmful radiation, drugs, dyes, or chemicals, and it can detect certain problems accurately and often rapidly. 

Combined with other tests and exams, ultrasound can help your health care provider make an accurate diagnosis and determine proper treatment for certain problems.  Ultrasound is often advised for women who may have problems during pregnancy.  It can enable your health care provider to monitor such problems more closely, helping to promote your good health and well-being.