Things That Might Show Up During An Ultrasound
What are the markers for Down Syndrome (Trisomy 21) that can be seen on ultrasound?
The expert answers
First, I want to point out that ultrasound cannot diagnose Down Syndrome. Down Syndrome is a chromosome disorder. Most humans have 46 chromosomes (23 pairs). A person with Down Syndrome has 47 chromosomes. They have three of chromosome number 21 instead of two.
The only way to confirm that a fetus has Down Syndrome is to do a genetic test, such as amniocentesis or chorionic villus sampling. That being said, ultrasound can be used to look for some of the signs of Down Syndrome. About 50 percent of fetuses with Down Syndrome will show abnormalities on the ultrasound. Therefore, a normal ultrasound does not exclude the possibility that the fetus could have Down Syndrome.
Some of the markers that we look for include:
- Increased nuchal skin fold thickness (measurement taken of the skin fold on the back of the neck)
- Heart defects
- "Double Bubble" sign (this indicates duodenal atresia, which is a gastrointestinal defect)
- Shortened femur/humerus measurement(these are the bones in the upper arm and the thigh)
- Hypoplasia of the middle phalanx of the fifth digit (shortened bone in the middle of the pinky finger)
- "Sandal Gap" (a wide space between the first and second toe)
- Pyelectasis (a dilation of the collecting system in the kidneys)
- Echogenic bowel pattern (a "bright" appearance of the bowel on ultrasound)
If one or more of these markers are seen, it does not mean that the fetus definitely has Down Syndrome. It means that there is an increased likelihood that the fetus may have Down Syndrome. Therefore further testing (usually in the form of an amniocentesis) would be offered.
Again, ultrasound can not diagnose or exclude the presence of Down Syndrome. Genetic testing, such as amniocentesis, is the only way to get conclusive results regarding Down Syndrome.