There are tests that can diagnose Down syndrome before a baby is born, but the condition is usually identified soon after birth.
A doctor may suspect a child has Down syndrome based on the child's appearance. 
According to the <a href="[BASEDOMAIN]/healthinfo/bouncelink.aspx?shortcut=modimes" target="_blank">March of Dimes</a>, some of the most common traits are: 
<ul>
 <li>Low muscle tone. </li>
 <li>A small nose with a flattened bridge. </li>
 <li>Eyes that have an upward slant. </li>
 <li>Small ears that may fold over a bit at the top. </li>
 <li>Small hands and feet.</li>
 <li>A short neck.</li>
 <li>A small mouth, which makes the tongue appear large. </li>
 <li>Short stature. </li>
</ul>
Most children with Down syndrome have some, but not all, of these traits, according to the March of Dimes. Some of these traits can also appear in babies who don't have Down syndrome.
If a doctor suspects&nbsp;Down syndrome, he or she will recommend a blood test to find out for sure.
Reviewed 8/21/2023

Diagnosing Down syndrome

What doctors look for.