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Fetal Ultrasound

Test Overview

Fetal ultrasound is a test done during pregnancy that uses reflected sound waves to produce a picture of a fetus, the organ that nourishes the fetus (placenta), and the liquid that surrounds the fetus (amniotic fluid). The picture is displayed on a TV screen and may be in black and white or in color. The pictures are also called a sonogram, echogram, or scan, and they may be saved as part of your baby's record.

Fetal ultrasound is the safest way to check for problems and get information about your fetus, such as its size and position. It does not use X-rays or other types of radiation that may harm your fetus. It can be done as early as the 5th week of pregnancy. The sex of your fetus can sometimes be determined by about the 18th week of pregnancy. For more information, see:

Click here to view a Decision Point.Pregnancy: Should I Have an Early Fetal Ultrasound?

A combination of screening tests using ultrasound may be done in the first trimester to look for Down syndrome. The integrated test uses an ultrasound measurement of the thickness of the skin at the back of the baby's neck (nuchal translucency) and the blood levels of free beta-HCG and a protein called pregnancy-associated plasma protein A (PAPP-A) to check for problems.

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  Pregnancy: Should I Have an Early Fetal Ultrasound?

Why It Is Done

Fetal ultrasound is done to learn about the health of the fetus. Different information is gained at different times (trimesters) during your pregnancy.

  • 1st-trimester fetal ultrasound is done to:
    • Determine how your pregnancy is progressing.
    • Find out if you are pregnant with more than 1 fetus.
    • Estimate the age of the fetus (gestational age).
    • Estimate the risk of a chromosome defect, such as Down syndrome.
    • Check for birth defects that affect the brain or spinal cord.
  • 2nd-trimester fetal ultrasound is done to:
    • Estimate the age of the fetus (gestational age).
    • Look at the size and position of the fetus, placenta, and amniotic fluid.
    • Determine the position of the fetus, umbilical cord, and the placenta during a procedure, such as an amniocentesis or umbilical cord blood sampling.
    • Detect major birth defects, such as a neural tube defect or heart problems.
  • 3rd-trimester fetal ultrasound is done to:
    • Make sure that a fetus is alive and moving.
    • Look at the size and position of the fetus, placenta, and amniotic fluid.

Transvaginal ultrasound is generally done early in a pregnancy to determine fetal age or to detect a suspected ectopic pregnancy. It is occasionally done late in pregnancy to determine the location of the placenta or in a high-risk pregnancy to monitor the length of the cervix.

How To Prepare

You may need a full bladder for the test. If so, you will be asked to drink water or other liquids just before the test and to avoid urinating before or during the test. Usually women in the third trimester do not need to have a full bladder.

For a transvaginal fetal ultrasound, the vaginal transducer is usually covered with a latex sleeve and a vaginal lubricant, such as K-Y Jelly. If you are allergic to latex, tell the health professional before having the test.

Talk to your doctor about any concerns you have regarding the need for the fetal ultrasound, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

How It Is Done

Most often, a fetal ultrasound is performed by an ultrasound technologist. But it may be done by a radiologist or obstetrician. Fetal ultrasound can be done in a doctor's office, hospital, or clinic.

See a picture of how a fetal ultrasound is done.

Often you do not need to remove your clothes for the ultrasound test. You can lift your shirt and push down the waistband of your skirt or pants. If you are wearing a dress, you will be given a cloth or paper covering to use during the test.

Transabdominal ultrasound

  • You may need to have a full bladder. A full bladder helps transmit sound waves and pushes the intestines out of the way of the uterus. This makes the ultrasound picture clearer.
    • You will not be able to urinate until the test is over. But tell the ultrasound technologist if your bladder is so full that you are in pain.
    • If an ultrasound is done during the later part of pregnancy, a full bladder may not be needed. The growing fetus will push the intestines out of the way.
  • You will lie on your back on a padded examination table. If you become short of breath or lightheaded while lying on your back, your upper body may be raised or you may be turned on your side.
  • A gel will be spread on your belly.
  • A small, handheld instrument called a transducer will be pressed against the gel on your skin and moved across your belly several times. You may watch the monitor to see the picture of the fetus during the test.

When the test is finished, the gel is cleaned off of your skin. You can urinate as soon as the test is done. Transabdominal ultrasound takes about 30 to 60 minutes.

Ultrasound technologists are trained to gather images of your fetus but cannot tell you whether it looks normal or not. Your health professional will share this information with you after the ultrasound images have been reviewed by a radiologist or perinatologist.

Transvaginal ultrasound

  • You do not need to have a full bladder.
  • You will lie on your back with your hips slightly raised.
  • A cover (such as a condom) will be placed over the thin vaginal transducer. The transducer will be inserted gently into your vagina, and then it will be moved and rotated to adjust the view displayed on the monitor. Some doctors may allow you to insert the transducer into your vagina yourself.

Transvaginal ultrasound takes about 15 to 30 minutes.

How It Feels

During a transabdominal ultrasound, you may have a feeling of pressure in your bladder. The gel may feel cool when it is first applied to your belly. You will feel a light pressure from the transducer as it passes over your belly.

There is normally no discomfort involved with a transvaginal ultrasound. You may feel a light pressure when the transducer is moved in your vagina.

Risks

There are no known risks associated with a fetal ultrasound, either to the mother or fetus. But you may feel anxious if the ultrasound reveals a problem with your pregnancy or fetus.

"Keepsake video operations" are ultrasound centers that sell ultrasound videos as your baby's first photo. The U.S. Food and Drug Administration (FDA) recommends ultrasound scans only to obtain medical information about the fetus. Keepsake video operations may use the ultrasound machine at higher energy levels and for longer times than needed to get a "good picture."

Results

A fetal ultrasound scan uses reflected sound waves to produce a picture of your fetus, the organ that nourishes your fetus (placenta), and the liquid that surrounds your fetus (amniotic fluid).

You may not receive information about the test right away. Full results are usually available in 1 or 2 days.

Fetal ultrasound
Normal:
  • The fetus is the size expected for its age.
  • The heart rate and breathing activity of the fetus is normal for its age.
  • If the test is done late in the pregnancy, the fetus is in the head-down position.
  • The placenta is the size expected for the stage of the pregnancy and does not cover the cervix.
  • The uterus contains an adequate amount of amniotic fluid.
  • No birth defects can be seen. (Many minor defects and some major defects are not easily seen. Also, birth defects do not always show up early in pregnancy.) See ultrasound images of a normal fetus.
Abnormal:
  • The fetus is growing more slowly than normal, is small, or is underdeveloped for its age.
  • The fetus is abnormally large for its age.
  • If this test is done late in the pregnancy, the fetus is in the buttocks-down (breech) position.
  • Birth defects, such as absent kidneys or anencephaly, are present.
  • The placenta covers the cervix (placenta previa).
  • The uterus contains too much or too little amniotic fluid.
  • The fetus is developing outside of the uterus (ectopic pregnancy).
  • The scan shows abnormal tissue instead of a normal fetus (molar pregnancy).
  • The fetal heartbeat is not present. This can mean fetal death.

Many conditions can change fetal ultrasound results. Your health professional will discuss any significant abnormal results with you in relation to your past health.

What Affects the Test

Fetal ultrasound results may be affected by:

  • Being very overweight or obese.
  • Stool (feces) or air in the intestines or rectum.
  • An abnormally low amount of amniotic fluid.
  • Some fetal positions.
  • Not being able to lie still during the procedure.
  • A very active fetus.

What To Think About

  • Normal fetal ultrasound results do not guarantee a normal, healthy baby.
  • Your doctor may recommend additional tests or procedures if the results of your fetal ultrasound are not normal.
  • A photograph or videotape of the ultrasound image of the fetus is sometimes available to you.
  • Your due date may be changed based on an ultrasound done in early pregnancy if the ultrasound predicts a different date, based on fetal size and development.
  • Ultrasounds do not always show birth defects.
  • In the third trimester, fetal ultrasound does not accurately determine fetal age or weight.
  • The effects of prolonged fetal ultrasound exposure have not been determined. So the U.S. Food and Drug Administration (FDA) does not recommend fetal ultrasound for nonmedical reasons, such as for identifying the sex of the fetus or as personal keepsakes.
  • Three-dimensional (3-D) fetal ultrasound is being tested for use in evaluating fetal abnormalities. It is not yet widely available.
  • Doppler ultrasound (or duplex scanning) uses reflected sound waves to estimate the speed and direction of blood as it flows to the placenta and within the fetus. For more information, see the topic Doppler Ultrasound.

Other Places To Get Help

Organization

American Congress of Obstetricians and Gynecologists (ACOG)
409 12th Street SW
P.O. Box 96920
Washington, DC  20090-6920
Phone: (202) 638-5577
Email: resources@acog.org
Web Address: www.acog.org
 

American Congress of Obstetricians and Gynecologists (ACOG) is a nonprofit organization of professionals who provide health care for women, including teens. The ACOG Resource Center publishes manuals and patient education materials. The Web publications section of the site has patient education pamphlets on many women's health topics, including reproductive health, breast-feeding, violence, and quitting smoking.

References

Other Works Consulted

  • American College of Obstetricians and Gynecologists (2009). Ultrasonography in pregnancy. ACOG Practice Bulletin No. 101. Obstetrics and Gynecology, 113(2): 451–461.
  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Credits

By Healthwise Staff
Primary Medical Reviewer Sarah Marshall, MD - Family Medicine
Specialist Medical Reviewer Kirtly Jones, MD - Obstetrics and Gynecology
Last Revised June 21, 2010

Last Revised: June 21, 2010

Author: Healthwise Staff

Medical Review: Sarah Marshall, MD - Family Medicine & Kirtly Jones, MD - Obstetrics and Gynecology

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