During the second trimester, ultrasound can be used to note markers
for increased likelihood of Down syndrome, but not all markers are
created equal. According to a study doctors should look for a specific set
of markers associated with the highest risk.
Over the last decade, new technology has improved the methods of detection of fetal abnormalities, including Down syndrome. Many but not all fetuses with Down syndrome have one or more so called 'markers' on ultrasound.