Your doctor may suggest that you have tests during pregnancy to find out if your baby has Down syndrome. You may decide to have:

Screening tests, such as an ultrasound or a blood test during your first or second trimester. These can help show if the developing baby (fetus) is at risk for Down syndrome. But these tests sometimes give false-positive or false-negative results.
Diagnostic tests, such as chorionic villus sampling or amniocentesis. These can show if a baby has Down syndrome. You may want to have these tests if you have abnormal results from a screening test or if you are worried about Down syndrome.
Sometimes a baby is diagnosed after birth. A doctor may have a good idea that a baby has Down syndrome based on the way the baby looks and the results of a physical exam. To make sure, the baby’s blood will be tested. It may take 2 to 3 weeks to get the test results.