How is Down syndrome diagnosed?

Your doctor may suggest that you have tests during pregnancy to find out if your baby has Down syndrome. A screening test can help show if the baby (fetus) is at risk for Down syndrome. But these tests sometimes give false-positive results, meaning they show a problem when there is none.

Screening tests include:

* A blood test and a fetal ultrasound late in the first trimester. The ultrasound looks for thickness in the back of the baby’s neck (nuchal fold), which can be a sign of Down syndrome. This kind of ultrasound is not available in many areas.
* A blood test called a maternal serum triple screen or quadruple screen in the second trimester. By measuring substances in your blood, these tests can estimate the chance that your baby has Down syndrome or other health problems.

Your doctor may suggest a chromosome (karyotype) test if you have an abnormal screening test result or if you are worried about Down syndrome. A karyotype test has more risks than a screening test, but it can say for sure if your baby has Down syndrome.

Karyotype tests include:

* Chorionic villus sampling in the first trimester. For this test, the doctor takes a sample of cells from the placenta, either by putting a thin tube through your vagina or by putting a thin needle into your belly.
* Amniocentesis in the second trimester. For this test, the doctor puts a thin needle into your belly and takes a sample of the liquid (amniotic fluid) that surrounds the baby.

Sometimes a baby is only 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 complete test results.