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Ultrasound Scanning in Pregnancy

What is ultrasound scanning?
Ultrasound scanning is a procedure that uses sound waves and their echoes to take pictures of structures inside the body. There is no x-ray radiation used during an ultrasound examination. It is a very safe test that will not hurt you or the baby.

When is it used in pregnancy?
Your healthcare provider uses ultrasound scanning to examine you and your pregnancy. In pregnancy, it is most commonly used to look at the baby, the placenta, the fluid around the baby, your uterus (womb), your ovaries and your cervix, which is the opening of the womb located at the top of the vagina.

Many pregnant women have one or more ultrasound scans as part of their routine prenatal care. You may also have ultrasound scans if your healthcare provider thinks there may be 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.

Some common reasons ultrasound scanning may be done during pregnancy are to:

  • Make sure the baby is developing in the uterus and not in a fallopian tube (ectopic pregnancy).
  • See how far along you are in your pregnancy and to confirm a due date.
  • Check the age, size, weight, and position of the baby.
  • See if the placenta is normal and attached properly.
  • Check for any problems with the uterus, such as an unusual shape or fibroids.
  • See if the baby's body has any major problems that might suggest a birth defect or genetic problem.
  • Check the amount of fluid around the baby inside the uterus.
  • Check for more than 1 baby. Check the baby's heart. Look at the baby's behavior, such as movements and practice breathing.
  • Help with an amniocentesis or other tests or procedures.
  • Check the baby for signs of stress as part of a biophysical profile.
  • Check into the cause of vaginal bleeding or pelvic pain.

An ultrasound scan may be done for different reasons at different stages in the pregnancy. For example, ultrasound examinations in the first or early second trimester (before 16 weeks) are very helpful to check the age of the baby, confirm the due date and check for more than 1 baby. Ultrasound examinations between 18 and 22 weeks are often used to examine the baby for any signs of a genetic problem or birth defect. Tests to see if the baby is growing at a normal rate are most accurate during the late second and third trimester of pregnancy.

Sometimes an ultrasound can tell whether the baby is a boy or a girl after 16 weeks gestational age. However, this is not usually the main reason for doing an ultrasound.

How do I prepare for ultrasound scanning?
Most of the time it is not necessary to have full bladder to have an ultrasound examination. However, every once in a while a full bladder is needed to see some structures in more detail. For this reason your provider may ask you to drink up to 6 glasses of water 1 hour before the test and then not to urinate until after the test. Your provider will tell you if this or other preparations are needed.

What happens during the procedure?
The ultrasound scan may be done at your provider's office, at a clinic or hospital, or at a radiology center.

A small device called a transducer probe is used to do the scan. The transducer acts like a microphone. During the scan, sound waves enter your body through the transducer. However, you should not expect to hear any of the sound waves. The transducer is connected to a computer. As the sound waves pass through your body, they are reflected back to the transducer by structures in the body, such as your organs or the baby. 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 an oil or gel on the skin of your abdomen. This helps the transducer glide smoothly over your skin and improves its contact with your body. Your provider will move the transducer over different parts of your abdomen to get pictures of the baby and the uterus.

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 protective cover that is like a condom. It is inserted gently into the vagina using a small amount of gel as a lubricant.

An abdominal ultrasound scan may take as long as an hour. A vaginal ultrasound is much quicker and usually takes much less than 5 minutes. You can sometimes watch the images of your baby on the screen as the examination is performed.

What happens after the procedure?
Usually you can go home and go back to your normal activities as soon as the scan is done. The results of the ultrasound may be given within a few minutes to a few days later.

What are the benefits of this procedure?
Ultrasound scans can improve a baby's chances of health and survival by:

  • Detecting possible problems that might be corrected before the baby is born.
  • Providing more accurate information about the baby's health before birth.
  • Preventing premature birth with a more accurate determination of the due date.
  • Providing information that can help determine if the baby can safely remain inside the uterus or whether the baby is showing signs that it would benefit from delivery.

There are no known side effects from ultrasound scanning. In addition, no medicines are known to interfere with test results. Ultrasound scanning is fast and painless. It does not use radiation and avoids possible hazards of some other tests used for diagnosis, such as bleeding, infection, or reactions to chemicals.

What are the risks of this procedure? Some women may feel a very small amount of discomfort from the pressure of the ultrasound transducer. However, there are no known physical risks associated with ultrasound scanning because the sound waves used are not dangerous.

Although ultrasound can tell us many things about a pregnancy, it is not a perfect test. It is uncommon, but possible to have a normal examination when the baby is affected by a problem. Even more uncommonly, a problem might be suspected when the baby is actually normal. Some things that might affect the accuracy of the examination include the baby's position, the gestational age, the amount of fluid around the baby, and how overweight the mother might be. Also, some women have tissue in their abdomen that prevents sound waves from passing easily, which makes it difficult to take clear pictures.

When should I call my healthcare provider?

  • Call your provider during office hours if:
  • You have questions about the procedure or its result.
  • You want to make another appointment.

Developed by RelayHealth.
Published by RelayHealth.
Last modified: 2008-08-11
Last reviewed: 2008-04-15
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.
Women's Health Advisor 2009.1 Index
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