Prenatal Ultrasound

A prenatal ultrasound test uses high-frequency sound waves, inaudible to the human ear, that are transmitted through the abdomen via a device called a transducer to look at the inside of the abdomen. With prenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby.

The ultrasound can be used during pregnancy to show images of the baby, amniotic sac, placenta, and ovaries. Major anatomical abnormalities or birth defects are visible on an ultrasound.

Most prenatal ultrasound procedures are performed topically, or on the surface of the skin, using a gel as a conductive medium to aid in the image quality. However, a transvaginal ultrasound is an alternative procedure in which a tubular probe is inserted into the vaginal canal. This method of ultrasound produces an image quality that is greatly enhanced. It may be used early in pregnancy to get a clearer view of the uterus or ovaries if a problem is suspected. It can also be used to determine how far along you are in your pregnancy (gestational age). Transvaginal ultrasound is also used to evaluate the cervix for problems such as shortening which may increase your risk of early labor.

Is Prenatal Ultrasound Safe?

All medical procedures have risk. But, there's no evidence to show a prenatal ultrasound done properly will harm a mother or her unborn child. Done properly means it's performed by a trained technician, called a sonographer. It also means using the lowest level of radiation needed to get what's asked for. Ultrasound does not use radiation, as other procedures, such as X-rays, do.

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When Is an Ultrasound Performed During Pregnancy?

An ultrasound is generally performed for all pregnant women around 20 weeks into her pregnancy. During this ultrasound, the doctor will confirm that the placenta is healthy and that your baby is growing properly in the uterus. The baby's heartbeat and movement of its body, arms and legs can also be seen on the ultrasound.

If you wish to know the gender of your baby, it can usually be determined by 20 weeks. Be sure to tell the health care provider performing the ultrasound whether or not you want to know the gender of your baby. Please note that ultrasound is not a foolproof method to determine your baby's gender; there is a chance that the ultrasound images can be misinterpreted.

An ultrasound may be performed earlier in your pregnancy to determine:

Later in pregnancy, ultrasound may be used to determine the:

  • Health of the baby
  • Placenta location
  • Amount of amniotic fluid around the baby
  • Position of the baby
  • Baby's expected weight

What Is a 3-D and 4-D Ultrasound?

Newer ultrasounds are now available that show a three-dimensional view of the fetus. This is similar in clarity to a photograph and can be useful in detecting birth defects when performed in a medical center. Some facilities are providing this scan at the parents' request without a specific medical indication. A moving picture interpretation is referred to as a 4-D ultrasound. According to the March of Dimes, the FDA, and other experts, the use of these non-medical ultrasounds is discouraged, because untrained personnel may provide inaccurate or harmful information.

How Should I Prepare for an Ultrasound?

There is no special preparation for the ultrasound test. Some doctors require you to drink 4-6 glasses of water before the test, so your bladder is full. This will help the doctor view the baby better on the ultrasound. You will be asked to refrain from urinating until after the test.

Some doctors allow you to videotape the ultrasound so that you can take it home. Ask your doctor if this is an option. If it is, you will need to bring a blank videotape or DVD to your appointment.

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What Happens During an Ultrasound?

You may be asked to change into a hospital gown.

You will lie on a padded examining table during the test and a small amount of water-soluble gel is applied to the skin over your abdomen. The gel does not harm your skin or stain your clothes.

A small device, called a transducer, is gently applied against the skin on your abdomen. The transducer sends high-frequency sound waves into the body, which reflect off internal structures, including your baby. The sound waves or echoes that reflect back are received by the transducer and transformed into a picture on a screen. These pictures can be printed out or sometimes recorded on a videotape.

There is virtually no discomfort during the test. If a full bladder is required for the test, you may feel some discomfort when the probe is applied over the bladder.

You may be asked to hold your breath briefly several times.

The ultrasound test takes about 30 minutes to complete.

What Happens After an Ultrasound?

The gel will be wiped off your skin and your health care provider will discuss the test results with you.

Will Insurance Pay for the Ultrasound?

Insurance will pay for the ultrasound if it is deemed medically necessary. If you have an ultrasound that is not medically necessary (for example, to simply see the baby or find out the baby's sex), your insurance company may not pay for the ultrasound.

WebMD Medical Reference Reviewed by Trina Pagano, MD on September 18, 2016

Sources

SOURCE: 

The March of Dimes.

© 2016 WebMD, LLC. All rights reserved.

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