Ultrasound has become a standard tool for pregnancy management and is increasingly being used to screen for Down syndrome. Most women will have one to two ultrasounds, if not more, over the course of their pregnancy for a variety of reasons. But what exactly does an ultrasound tell us, and how exactly does it work? Read this article to get an idea of what an ultrasound is and how it relates to Down syndrome.
How Does An Ultrasound Work?
Ultrasound works by using sound waves (too high for the human ear to hear) to generate an image of the fetus. A special gel is put on the mother’s abdomen and a transducer, a wand like apparatus, is used to transmit the sound waves into the abdomen. The sound waves travel through the amniotic fluid and bounce off of structures located in the uterus. The sound waves bounce back at different speeds depending on the density of the structure that 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, and having a great deal of knowledge of fetal anatomy, a qualified healthcare professional is able to examine your baby’s anatomy.
Ultrasound has been routinely used in pregnancy since the 1960s. Based on a large number of medical studies, there are no known health risks to the fetus or mother associated with routine use of prenatal ultrasound.
What Are Some Reasons that Women Have Ultrasounds During Pregnancy?
There are many reasons that you may have an ultrasound during your pregnancy. In the first trimester, ultrasound can determine the expected delivery date of the baby, find out if there is more than one baby in the womb, check the location and development of the placenta, determine if there has been a miscarriage, and detect or screen for birth defects such as Down syndrome. Ultrasound is also used during diagnostic prenatal testing procedures and for many other reasons.
Can an Ultrasound Diagnose Down Syndrome?No, an ultrasound cannot diagnose a fetus with Down syndrome. However, ultrasound is sometimes used as a screening test for Down syndrome and other chromosome abnormalities. Certain findings (sometimes called soft markers) on an ultrasound may make your physician or healthcare provider suspicious that your baby may have Down syndrome. Soft markers are findings that, in and of themselves, won’t cause the baby any problems but might indicate that the baby has an underlying chromosome abnormality.
What Are Some Common Soft Markers for Down Syndrome?
Soft markers for Down syndrome include (but are not limited to):
- Increased nuchal translucency
- Shortened femur length
- Choroid plexus cysts
- Intracardiac echogenic foci
- Echogenic bowel
- Single umbilical artery
- Dilated renal pelvis
What Should I Do If One of These Markers is Seen on My Ultrasound?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 CVS test or an amniocentesis. These tests are optional during pregnancy, and each woman must decide for herself if she wants to have this testing.
The Bottom Line
Even if one of these markers is seen during your ultrasound, it is important to remember that most babies found to have one of these markers turn out to be perfectly healthy babies with no underlying chromosome abnormalities. Ultrasound is just a screening test and cannot diagnose Down syndrome or other chromosome abnormalities.
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.