McKesson Clinical Reference Systems: Women's Health Advisor 2002.2

What is ultrasound scanning?

Ultrasound scanning is a procedure that uses high-frequency sound waves to create a picture of organs in the body.

When is it used in pregnancy?

Your health care provider uses ultrasound scanning to examine your unborn baby. He or she also uses it to look at your uterus, amniotic sac, placenta, and ovaries.

Many health care providers use ultrasound routinely at certain stages of pregnancy. They also may use it if they suspect a problem with the pregnancy or if you have risk factors that could lead to problems for the baby. Ultrasound scanning is very helpful for many abnormal conditions.

Ultrasound scanning is used in pregnancy to:

• Make sure the baby is developing in the uterus and not inside a fallopian tube (ectopic pregnancy).
• Determine how far along you are in your pregnancy.
• Check that the baby is growing normally.
• Estimate the weight of the baby.
• See if the placenta is normal and attached properly.
• Check the position of the baby in the uterus.
• See if the baby's body has any major problems.
• Check the amount of fluid around the baby inside the uterus.
• Check for more than one baby.
• Check the baby's heart.
• Look for movement by the baby and breathing movements of the baby's chest.
• Get accurate measurements of the baby, including:
  • the length of the thighbone
  • the diameter of the head
  • the size of the abdomen.
• Help with an amniocentesis.
• Check the baby for signs of stress as part of a biophysical profile.

An ultrasound scan may be done for different reasons at different stages in the pregnancy. For example, tests to see if the baby is growing at a normal rate are most accurate during the second trimester of pregnancy. To check the age of the baby or check for more than one baby, an ultrasound is often done between the 16th and 20th weeks.

Sometimes a baby's gender may be learned by looking for the genitals in an ultrasound scan after the 16th week of pregnancy. However, this is not usually a reason for doing an ultrasound.

How do I prepare for ultrasound scanning?

If your bladder is full, it may be easier for your health care provider to see the baby and other organs. For this reason your health care provider may ask you to drink up to 6 glasses of water an hour before the test and then not to urinate until after the test. Your provider will tell you if this or any other preparations are necessary.

What happens during the procedure?

A device called an ultrasound transducer is used to do the scan. The transducer acts like a microphone. During the scan, high-frequency sound waves enter your body through the transducer. The transducer is connected to a computer. As the sound waves pass through your body, they are reflected by the organs and create echoes. The computer analyzes these echoes and produces images of the organs on a screen.

The ultrasound exam may be done by putting the transducer on the surface of your abdomen. First your provider or the ultrasound technologist will put a jellylike substance on the skin of your abdomen. Then he or she will place the transducer on your abdomen. The transducer will be moved over different parts of your abdomen so that the entire uterus and baby can be viewed.

Some ultrasound exams, especially early in pregnancy, are done through the vagina. For these scans the transducer is shaped like a narrow tube and covered with a condomlike sheath. It is inserted gently into the vagina.

An ultrasound scan does not hurt you or your baby. It takes about 15 minutes. You can watch the images of your baby on the screen.

When should I call my health care provider?

Call your health care provider during office hours if:

• You have questions about the procedure or its result.
• You want to make another appointment.

This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.