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Children's Health

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Understanding Down Syndrome -- Diagnosis and Treatment

How Do I Know If My Child Has Down Syndrome? continued...

Diagnostic Tests

Diagnostic tests use a direct sample of the baby’s genetic material. They can tell with almost 100% accuracy whether or not your baby has Down syndrome.

If a screening test shows an increased chance of Down syndrome, you may choose to have a diagnostic test during pregnancy. You can also request a diagnostic test without having a screening. Unlike screening tests, these tests have a small chance of harming babies still in the womb. A needle needs to be inserted in the mother’s womb to collect the material for testing. This raises the risk of miscarriage (the risk ranges from less than 1% to around 2%,).

A baby can have diagnostic testing after delivery, too.

The different diagnostic tests during pregnancy are:

Amniocentesis: This test cannot be performed before the 14th week of pregnancy. It's usually done between weeks 14 and 18. It uses a sample of the fluid in the mother’s womb.

Chorionic villus sampling: This test takes a sample from the placenta. It's performed between 9 and 11 weeks of pregnancy.

Percutaneous umbilical blood sampling (PUBS): This test takes a sample of the baby’s blood from the umbilical cord. It is the most accurate of the three tests, but it can't be performed until you are at least 18 weeks pregnant.

After you have your baby, a doctor will do a physical exam and test the baby’s blood to diagnose Down syndrome.

A genetic counselor can help you understand the results of your tests.

What You Need to Know

Down syndrome happens at the time of pregnancy. Nothing you do or don’t do while pregnant can cause it. People with this condition have an extra chromosome, the part of a cell that has genes.

The risk of having a baby with the condition goes up with the mother’s age. At age 20, a woman has a 1 in 2,000 chance of having a baby with Down syndrome. By age 35, that risk is 1 in 350.

Very few cases of Down syndrome -- only about 1% -- are “hereditary,” or passed down from a parent to their child through the genes. If your sister or brother, aunt or uncle has Down syndrome, there’s very little chance you’ll have a baby with it. But if a woman has had a baby with Down syndrome, her chance of having another child with the condition is higher.

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