Can Down Syndrome Be Diagnosed With an Ultrasound?

Your ultrasound results can provide insight into your child's development

Photo of pregnant woman
Ultrasound in pregnancy. K. Fergus

Ultrasounds provide a great way to monitor your pregnancy and can be used to screen for Down syndrome. You will most likely have at least one or two ultrasounds, if not more, over the course of your pregnancy to monitor your child's growth and development. 

There are many reasons why you may have an ultrasound during your pregnancy. During your first trimester, an ultrasound can help determine your baby's due date, whether you are pregnant with one or multiple babies, the location and development of your placenta as well as if you have had a miscarriage.

Ultrasounds can also be used during diagnostic prenatal testing procedures and can help doctors detect potential birth defects. 

How Does An Ultrasound Work?

Ultrasounds work by using sound waves too high for the human ear to hear to generate an image of the fetus. When performing an ultrasound, your doctor will rub a special gel your abdomen and use a transducer, a wand-like apparatus, to transmit the sound waves into your abdomen. These waves pose no risk to you or your child. 

The sound waves travel through the amniotic fluid and bounce off of structures located in the uterus. These waves bounce back at different speeds depending on the density of the structures they hit before deflecting. A computer then turns these returning sound waves into an image of the fetus. The harder or denser a structure is, the brighter it will show up on the monitor.

For example, when looking at a fetal ultrasound, bony structures such as the skull and leg bones show up bright white.

Less dense organs, such as the liver and kidneys, show up as light gray. Amniotic fluid shows up as black because the sound waves go straight through the fluid and don’t bounce back. By looking at these black and white images, a qualified healthcare professional can examine your baby’s anatomy.

Can an Ultrasound Diagnose Down Syndrome?

An ultrasound cannot diagnose Down syndrome.

However, it can provide information about your child that might make your doctor more inclined to test for Down syndrome and other chromosomal abnormalities. Certain ultrasound findings, sometimes called soft markers, are findings that, in and of themselves, won’t cause the baby any problems but might indicate an underlying chromosome abnormality. Soft markers for Down syndrome may include: 

  • Increased nuchal translucency: Nuchal translucency measures how thick the fluid buildup at the back of your developing child's neck is. If the area is thicker than average, it may be a sign of Down syndrome. 
  • Shortened femur length: A shortened femur, or thigh bone, can be another sign. 
  • Choroid plexus cysts: This type of cyst occurs in the fetal brain. 
  • Intracardiac echogenic foci: Representing mineralizations in the muscles of the heart, this is a more common ultrasound finding. 
  • Echogenic bowel: This soft marker shows the bowel as being brighter than it is supposed to be. 
  • Single umbilical artery: Most umbilical cords have one vein and two arteries. 
  • Dilated renal pelvis: Also a common ultrasound finding, a dilated renal pelvis, or hydronephrosis, means the area of the pelvis by the kidneys is distended. 

    Further Testing for Down Syndrome

    If any of these markers are found on your ultrasound, you should speak with your doctor or healthcare provider to determine your risk of having a baby with a chromosome abnormality and to discuss what further prenatal testing you may want to consider.

    The only way to tell if your baby has an underlying chromosome abnormality is to have a prenatal diagnostic test such as a chorionic villus sampling (CVS) test or an amniocentesis. These tests are optional but can help you determine your child's future health. 

    Even if one of these markers is seen during your ultrasound, it is important to remember that many babies with one of these markers turn out to be perfectly healthy babies with no underlying chromosome abnormalities.

    Ultrasounds are just a screening test and cannot diagnose Down syndrome or other chromosome abnormalities.

    Sources:

    ACOG Committee on Practice Bulletins. ACOG Practice Bulletin No. 77: Screening for fetal chromosomal abnormalities. Obstet Gynecol. 2007 Jan;109(1):217-27.

    Newberger, D., Down Syndrome: Prenatal Chance Assessment and Diagnosis. American Family Physician. 2001.

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