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Fetal Ultrasound

Test Overview

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

Fetal ultrasound can be done two ways. In a transabdominal ultrasound, a small handheld device called a transducer is moved over your belly. In a transvaginal ultrasound, a transducer is put into your vagina.

Fetal ultrasound is the safest way to check for problems and get details about your fetus. It can find things such as the size and position of the fetus. 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. Sometimes the sex of your fetus can be seen by about the 18th week of pregnancy.

Ultrasound is one of the screening tests that may be done in the first trimester to look for birth defects, such as Down syndrome. The first-trimester screening test uses ultrasound to measure the thickness of the skin at the back of the baby's neck. This screening also includes blood tests that measure the levels of two substances that may be related to birth defects.

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Why It Is Done

Fetal ultrasound is done to learn about the health of your fetus. Different details can be learned at different times during your pregnancy.

First trimester ultrasound

This test is done to:

  • See how your pregnancy is going.
  • Find out if you are pregnant with more than one 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.

Second trimester ultrasound

This test is done to:

  • Estimate the age of the fetus.
  • Look at the size and position of the fetus, placenta, and amniotic fluid.
  • Check the position of the fetus, umbilical cord, and placenta during a procedure such as amniocentesis or umbilical cord blood sampling.
  • Find major birth defects, such as a neural tube defect or heart problems.

Third semester ultrasound

This test 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.

Learn more

How To Prepare

In general, there's nothing you have to do before this test, unless your doctor tells you to.

How It Is Done

Fetal ultrasound can be done in a doctor's office, hospital, or clinic.

You may be able to leave your clothes on, or you will be given a gown to wear.

Transabdominal ultrasound

  • You may need to have a full bladder. A full bladder helps transmit sound waves, and it 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 tech 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 an exam table. If you become short of breath or feel faint 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 device called a transducer will be pressed against the gel on your skin. It will be moved across your belly several times. You may watch the monitor to see the picture of the fetus during the test.

You can urinate as soon as the test is done.

Ultrasound techs are trained to gather images of your fetus. But they can't tell you if it looks normal or not. Your doctor 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 knees bent and feet and legs supported by footrests.
  • A cover (such as a condom) will be placed over the thin transducer. The transducer will be put gently into your vagina. It will be moved to adjust the image on the monitor. Some doctors may let you to put the transducer into your vagina yourself.

How long the test takes

  • A transabdominal ultrasound takes about 30 to 60 minutes.
  • A transvaginal ultrasound takes about 15 to 30 minutes.
  • A second-trimester fetal ultrasound takes about 30 to 60 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 put on your belly. You will feel a light pressure when the transducer is passed over your belly.

Normally a transvaginal ultrasound does not cause discomfort. You may feel a light pressure when the transducer is moved in your vagina.

Risks

There are no known risks from having this test.

"Keepsake video operations" are ultrasound centers that sell ultrasound videos as your baby's first photo. The U.S. Food and Drug Administration (FDA) does not recommend ultrasounds for this reason. It recommends ultrasounds only to obtain medical information about a fetus. Keepsake centers may use the ultrasound machine at higher energy levels and for longer times than needed in order to get a "good picture."

Results

You may not get details 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 are normal for the age of the fetus.
  • 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.
  • The uterus has the right amount of amniotic fluid.
  • No birth defects can be seen. (Many minor defects and some major defects are not easy to see. Also, birth defects do not always show up early in pregnancy.)

Abnormal:

  • The fetus is growing more slowly than normal, is small, or is less developed than it should be 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 seen.
  • The placenta covers the cervix (placenta previa).
  • The uterus has too much or too little amniotic fluid.
  • The fetus is growing outside of the uterus (ectopic pregnancy).
  • The scan shows abnormal tissue instead of a normal fetus (molar pregnancy).
  • No heartbeat is present. This can mean that it's too early to see a heartbeat. Or it might mean fetal death.

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

Credits

Current as of: October 8, 2020

Author: Healthwise Staff
Medical Review:
Sarah Marshall MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
William Gilbert MD - Maternal and Fetal Medicine
Femi Olatunbosun MB, FRCSC - Obstetrics and Gynecology

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