Down syndrome frequently is suspected at birth based on physical appearance. The diagnosis usually is confirmed by a blood test to examine the chromosomes. Additional testing may be done, including chest X-rays, echocardiography and an electrocardiogram, to check for heart problems. Sometimes X-ray studies of the gastrointestinal tract are done as well.
In some cases, Down syndrome is suspected during pregnancy from the results of a fetal ultrasound and blood test that measures the levels of three chemicals (a "triple-screen" test) in a pregnant woman's blood. If these results are abnormal, further tests can be done to help diagnose Down syndrome.