URL of this page: https://medlineplus.gov/lab-tests/down-syndrome-tests/

Down Syndrome Tests

What are Down syndrome tests?

Down syndrome is a disorder that causes intellectual disabilities, distinctive physical features, and various health problems. These may include heart defects, hearing loss, and thyroid disease. Down syndrome is a type of chromosomal disorder.

Chromosomes are the parts of your cells that contain your genes. Genes are parts of DNA passed down from your mother and father. They carry information that determines your unique traits, such as height and eye color.

  • People normally have 46 chromosomes, divided into 23 pairs, in each cell.
  • One of each pair of chromosomes comes from your mother, and the other pair comes from your father.
  • In Down syndrome, there is an extra copy of chromosome 21.
  • The extra chromosome changes the way the body and brain develop.

Down syndrome, also called trisomy 21, is the most common birth defect in the United States.

In two rare forms of Down syndrome, called mosaic trisomy 21 and translocation trisomy 21, the extra chromosome doesn't show up in every cell. People with these disorders usually have fewer of the characteristics and health problems associated with the common form of Down syndrome.

Down syndrome screening tests show whether your unborn baby is more likely to have Down syndrome. Other types of tests confirm or rule out the diagnosis.

What are the tests used for?

Down syndrome tests are used to screen for or diagnose Down syndrome. Down syndrome screening tests have little or no risk to you or your baby, but they can't tell you for sure whether your baby has Down syndrome.

Diagnostic tests during pregnancy can confirm or rule out a diagnosis, but the tests have a small risk of causing a miscarriage.

Why do I need a Down syndrome test?

Many health care providers recommend Down syndrome screening and/or diagnostic tests for pregnant women who are 35 years of age or older. A mother's age is the primary risk factor for having a baby with Down syndrome. The risk increases as a woman gets older. But you may also be at higher risk if you've already had a baby with Down syndrome and/or have a family history of the disorder.

In addition, you may want to get tested to help you prepare if the results show your baby may have Down syndrome. Knowing in advance can give you time to plan for health care and support services for your child and family.

But testing isn't for everyone. Before you decide to get tested, think about how you'd feel and what you might do after learning the results. You should discuss your questions and concerns with your partner and your health care provider.

If you didn't get tested during pregnancy or want to confirm the results of other tests, you may want to have your baby tested if he or she has symptoms of Down syndrome. These include:

  • Flattened face and nose
  • Almond-shaped eyes that slant upward
  • Small ears and mouth
  • Tiny white spots on the eye
  • Poor muscle tone
  • Developmental delays

What are the different types of Down syndrome tests?

There are two basic types of Down syndrome tests: screening and diagnostic tests.

Down syndrome screening includes the following tests done during pregnancy:

  • First trimester screening includes a blood test that checks the levels of certain proteins in the mother's blood. If levels are not normal, it means there is a higher chance of the baby having Down syndrome. The screening also includes an ultrasound, an imaging test that looks at the unborn baby for signs of Down syndrome. The test is done between the 10th and 14th week of pregnancy.
  • Second trimester screening. These are blood tests that also look for certain substances in the mother's blood that may be a sign of Down syndrome. A triple screen test looks for three different substances. It is done between the 16th and 18th week of pregnancy. A quadruple screen test looks for four different substances and is done between the 15th and 20th week of pregnancy. Your provider may order one or both of these tests.

If your Down syndrome screening shows a higher chance of Down syndrome, you may want to take a diagnostic test to confirm or rule out a diagnosis.

Down syndrome diagnostic tests done during pregnancy include:

  • Amniocentesis, which takes a sample of amniotic fluid, the fluid that surrounds your unborn baby. It is usually done between the 15th and 20th week of pregnancy.
  • Chorionic villus sampling (CVS), which takes a sample from the placenta, the organ that nourishes your unborn baby in your uterus. It's usually done between the 10th and 13th week of pregnancy.
  • Percutaneous umbilical blood sampling (PUBS), which takes a blood sample from the umbilical cord. PUBS gives the most accurate diagnosis of Down syndrome during pregnancy, but it can't be done until late in pregnancy, between the 18th and 22nd week.

Down syndrome diagnosis after birth:

Your baby may get a blood test that looks at his or her chromosomes. This test will tell you for sure whether your baby has Down syndrome.

What happens during Down syndrome testing?

During a blood test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

For the first trimester ultrasound, a health care provider will move an ultrasound device over your abdomen. The device uses sound waves to look at your unborn baby. Your provider will check for thickness at the back of your baby's neck, which is a sign of Down syndrome.

For amniocentesis:

  • You'll lie on your back on an exam table.
  • Your provider will move an ultrasound device over your abdomen. Ultrasound uses sound waves to check the position of your uterus, placenta, and baby.
  • Your provider will insert a thin needle into your abdomen and withdraw a small amount of amniotic fluid.

For chorionic villus sampling (CVS):

  • You'll lie on your back on an exam table.
  • Your provider will move an ultrasound device over your abdomen to check the position of your uterus, placenta, and baby.
  • Your provider will collect cells from the placenta in one of two ways: either through your cervix with a thin tube called a catheter, or with a thin needle through your abdomen.

For percutaneous umbilical blood sampling (PUBS):

  • You'll lie on your back on an exam table.
  • Your provider will move an ultrasound device over your abdomen to check the position of your uterus, placenta, baby, and umbilical cord.
  • Your provider will insert a thin needle into the umbilical cord and withdraw a small blood sample.

Will I need to do anything to prepare for the tests?

There are no special preparations needed for Down syndrome testing. But you should talk to your health care provider about the risks and benefits of testing.

Are there any risks to the tests?

There is very little risk to having a blood test or ultrasound. After a blood test, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Amniocentesis, CVS, and PUBS tests are usually very safe procedures, but they do have a slight risk of causing a miscarriage.

What do the results mean?

Down syndrome screening results can only show if you have a higher risk of having a baby with Down syndrome, but they can't tell you for sure if your baby has Down syndrome You may have results that are not normal, but still deliver a healthy baby with no chromosomal defects or disorders.

If your Down syndrome screening results were not normal, you may choose to have one or more diagnostic tests.

It can help to speak to a genetic counselor before testing and/or after you get your results. A genetic counselor is a specially trained professional in genetics and genetic testing. He or she can help you understand what your results mean.

Is there anything else I need to know about Down syndrome tests?

Raising a child with Down syndrome can be challenging, but also rewarding. Getting help and treatment from specialists early in life can help your child reach his or her potential. Many children with Down syndrome grow up to lead healthy and happy lives.

Talk to your health care provider and genetic counselor about specialized care, resources, and support groups for people with Down syndrome and their families.

References

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The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.