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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, but it is not a common prenatal procedure. However, it may be used early in pregnancy to get a clearer view of the uterus or ovaries if a problem is suspected. It may also be used early in pregnancy to determine how far along you are in your pregnancy (gestational age).

Is Prenatal Ultrasound Safe?

Studies have shown ultrasound is not hazardous. There are no harmful side effects to you or your baby. In addition, ultrasound does not use radiation, as X-ray tests do.

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:

  • Presence of more than one fetus
  • Your due date or gestational age (the age of the fetus)

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.

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