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Fetal ultrasound is a test used during pregnancy. It creates an image of the baby in the mother's womb (uterus). It’s a safe way to check the health of an unborn baby. During a fetal ultrasound, the baby’s heart, head and spine are evaluated, along with other parts of the baby. The test may be done either on the mother’s abdomen (transabdominal) or in the vagina (transvaginal).
There are several types of fetal ultrasound:
- Standard ultrasound. The test uses sound waves to create 2-D images on a computer screen.
- Doppler ultrasound. This test shows and measures the movement of blood through the uterus, umbilical cord, in the baby’s heart or around the baby's body.
- 3-D ultrasound. This test shows a lifelike image of an unborn baby.
Ultrasound uses an electronic wand called a transducer to send and receive sound waves. No radiation is used during the procedure. The transducer is moved over the abdomen, and sound waves move through the skin, muscle, bone and fluids at different speeds. The sound waves bounce off the baby like an echo and return to the transducer. The transducer converts the sound waves into an electronic image on a computer screen.
Fetal ultrasound is a routine part of prenatal care in the U.S. This is because it’s a low risk procedure that gives important information. A routine prenatal ultrasound can check for defects or other problems in the unborn baby. The following can be examined:
- Abdomen and stomach
- Arms, legs and other body parts
- Back of the neck
- Head and brain
- Heart chambers and valves
- Placenta placement
- Umbilical cord
- Urinary bladder
A fetal ultrasound can also show:
- If a woman is pregnant with multiple babies
- The gestational age of a baby
- Where to place the needle during removal of amniotic fluid (amniocentesis)
- Whether a baby is growing normally
Your health care provider may have other reasons to request a fetal ultrasound.
All procedures have some risks. The risks of this procedure include:
- Mild discomfort from the transducer on the abdomen or in the vagina
- Reaction to a latex covering for the transducer, if you have a latex allergy
In some cases, an ultrasound may appear to show a problem that is not there called false-positive. The test can also miss a problem that is there called false-negative. In some cases, additional testing may be needed after a fetal ultrasound.
Fetal ultrasound is sometimes offered in nonmedical settings. This is done as a way to give keepsake images or videos for parents. In these cases, it’s possible for untrained staff to misread the images and give parents incorrect information. Make sure to have fetal ultrasound done by trained medical staff. Talk with your health care provider if you have questions.
Your risks may vary depending on your general health and other factors. Ask your health care provider which risks apply most to you. Discuss any concerns you may have.
Your health care provider will explain the procedure to you. Ask any questions you may have. You may be asked to sign a consent form that gives permission to do the procedure. Read the form carefully. Ask questions if anything is not clear.
Tell your health care provider if you:
- Are sensitive to or allergic to any medicines, latex, tape or anesthetic medicines (local and general)
- Take any medicines, including prescriptions, over-the-counter medicines, vitamins and herbal supplements
You may be asked to drink several glasses of water before the procedure. This can help give clearer images.
You may have your procedure as an outpatient. This means you can go home the same day. Or it may be done as part of a longer stay in the hospital. The way the procedure is done may vary. It depends on your condition and your health care provider’s methods. In most cases, the procedure will follow this process:
- If you are having a transabdominal ultrasound, you will be asked to raise your shirt to expose your abdomen. For a transvaginal ultrasound, you will be asked to remove your clothes from the waist down. You will be given a sheet to place over your legs. You may be asked to remove jewelry or other objects.
- You will lie on an exam table, either on your back or on your side.
- For a transabdominal procedure, a clear gel will be placed on the skin of your belly (abdomen). The transducer will be moved over the area and pressed against the skin.
- For a transvaginal ultrasound, you will need to lie on your back. Your feet will be in stirrups and your knees apart.
- A vaginal transducer probe will be covered with a sterile cover. A lubricant will be put on the probe. The probe will be inserted into the vagina. The technician will move the probe around to capture a series of images. The probe will then be removed.
You will be given tissue to wipe off excess gel. You can go home shortly after the test. Your health care provider will talk with you about the results. You may get other instructions after the procedure.
Division Chief, Diagnostic Imaging and Radiology
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