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Pregnancy Ultrasound

Bryan Jick, MD, FACOG

Reviewed by
Bryan Jick, MD, FACOG

For expectant parents, an ultrasound provides the opportunity to view the baby and connect with him or her before birth. For your doctor, an ultrasound provides a chance to evaluate the baby’s growth and development. Ultrasound is considerably safer than other imaging methods, such as x-rays or CT scans, because it does not involve subjecting the patient to ionizing radiation.

What’s an Ultrasound?

Ultrasounds are also called sonograms, which means that sound is involved. High frequency (and very low energy) sound waves are produced by a transducer (which looks like a wand). A special gel is applied to the mother’s abdomen and the transducer is rubbed on top of it. Sound waves penetrate the body and echoes are generated and sent back to the transducer. They are transformed into electrical impulses and an image is created and displayed on a computer monitor.

Ultrasound should be performed only when there is a medical reason to do so and by people with appropriate training, according to various professional groups such as the American Institute of Ultrasound in Medicine (AIUM), the American College of Obstetricians and Gynecologists (ACOG) and the American College of Radiology (ACR).

Why Are Ultrasounds Done?

Pregnancy ultrasounds are performed for a variety of reasons:

  • To diagnose pregnancy
  • To determine if the pregnancy is viable
  • To verify that the pregnancy is in the proper location and not ectopic or “tubal”
  • To determine whether the mother is carrying more than one fetus
  • To verify the gestational age of the fetus, and thus to help establish the due date
  • To detect birth defects (though not all birth defects are detectable using ultrasound)
  • To ensure that there is not too much or too little amniotic fluid around the baby
  • To monitor fetal growth and heartbeat
  • To verify presentation (is the baby coming head first?) and make sure the baby is not in a breech position
  • To analyze the blood flow through the umbilical cord
  • To establish the anatomy of the placenta and how the cord inserts into the placenta
  • To detect pregnancy-related tumors (very rare!)

Types of Ultrasounds

There are a several different types of ultrasounds, and they are performed for different reasons during the course of your pregnancy.

  • Standard 2-D: This is the most commonly performed ultrasound. The images are in two dimensions, the standard for viewing on a video screen. Nearly all of the above tests (such as verification of gestational age, number of babies, and anatomy survey) can be performed with this technology. The procedure usually lasts about 20 minutes.
  • Advanced Ultrasound (also called level II or targeted ultrasound): This is similar to the standard ultrasound, but the purpose is to target suspected problems. This can take as little as 30 minutes or as long as a few hours to perform.
  • Transvaginal Ultrasound: A special long and narrow transducer, protected by a single-use cover or sheath, is introduced into the vagina to send out sound waves and gather reflections. It’s mostly done in the early stages of pregnancy. The main advantage is improved imaging because the transducer is much closer to the structures being investigated than it would be using the abdominal approach. The trade-off is not as much depth of imaging. Unlike the standard ultrasound, a transvaginal ultrasound is usually performed on an empty bladder.
  • 3-D/4-D Ultrasounds: The computer collects several 2-D images and creates a three-dimensional image from them. This does not replace 2-D ultrasound, but it can be useful for detecting certain conditions, such as cleft lip or palate for example. It is not performed as a matter of routine, however. When 3-D is viewed in real time with movements, it is called 4-D. This can be useful when there are concerns about the baby’s limb movements or position. If the baby is in a good position and there is enough fluid, an image of the face can sometimes be obtained.
  • Doppler Imaging: This test measures changes in the ultrasound waves as they bounce off moving objects such as blood cells. It is very useful for evaluating fetal circulation to determine whether there is any resistance or impairment to the flow of blood through the cord.

What to Expect During Your Ultrasound Procedure

Your pregnancy ultrasound will most likely be conducted in the radiology department of a hospital or in an exam room in your Ob/Gyn doctor’s office. Because getting the best possible image requires you to have a full bladder, you will be given a few glasses of water an hour or so before the test—or you will be instructed to arrive with a full bladder and asked to hold it till the exam!

When it is time to begin the procedure, a technician will cover your belly and pelvic area with a clear, water-based gel that helps to prevent the formation of air pockets between your body and the transducer. The technician will move the transducer around over your abdomen, and the sound waves it produces will bounce off the structures in your body—including the baby.

The transducer picks up these returning sound waves and the computer forms an image from them in much the same way that a bat or dolphin forms mental images of its surroundings by echolocation. The sound waves produced are at a frequency well above the range of human hearing, so neither you nor the baby will hear them or feel anything at all.

Are Ultrasounds Safe?

Ultrasound is a form of energy. As such, theoretically it can affect tissue when it is used. The two major effects are thermal—there can be a slight increase in temperature—and mechanical, as a result of pressure changes when the waves pass through. These effects are not harmful if the examination is performed correctly with equipment in good working condition. In fact, as far as is known, ultrasound is completely safe as long as a trained caregiver such as an obstetrician, sonographer, or radiologist is involved.

It is very important not only to properly perform the ultrasounds, but also to effectively interpret the information obtained with them. Ultrasounds can be unsafe if the machines are not operated by medical professionals; an untrained operator may use higher power levels than necessary. This sometimes occurs at facilities that offer ultrasounds for non-medical reasons, like selling videos or portraits to parents. It’s important as an expectant parent to know the medical credentials of anyone performing an ultrasound during your pregnancy.

Still have questions about Ultrasounds? See what others are saying in our forums! It’s easy and free to join the conversation!

Medical References:

    The National Institutes of Health http://www.nlm.nih.gov/medlineplus/ency/article/003778.htm http://www.nlm.nih.gov/medlineplus/ency/article/003779.htm The Mayo Clinic http://www.mayoclinic.org/tests-procedures/ultrasound/basics/definition/prc-20020341
[Page updated November 2014]