Patient education: Testing for Down syndrome during pregnancy (The Basics)

What is Down syndrome? — Down syndrome is a condition that happens when a person is born with an extra chromosome. Chromosomes are tiny parts of cells that carry the plans that make our bodies the way they are.

Typically, people are born with 23 pairs of chromosomes, giving them 46 in total. People with Down syndrome have an extra copy of chromosome 21. This can be a full or partial extra copy. When someone has a full extra copy, meaning they have 47 chromosomes in total, it is called "trisomy 21."

Down syndrome causes intellectual disability. This can make it more difficult for a person to learn, communicate, and do certain tasks. It can also cause medical problems affecting the heart, blood, digestive system, and other organs. The level of disability in people with Down syndrome can range from mild to severe.

About 1 to 2 in 1000 babies in the US are born with Down syndrome. As you get older, your chances of giving birth to a baby with Down syndrome get higher. But it can happen at any age.

What are my options for Down syndrome testing during pregnancy? — During pregnancy, you can choose to have:

●Screening tests – These are tests that can tell you if it is likely that your baby has Down syndrome. But they do not tell you for sure.

●Diagnostic tests – These are tests that can tell you for sure if your baby has Down syndrome.

You can also choose not to have screening or diagnostic tests.

What do the screening tests involve? — Different screening tests are available depending on how far along you are in your pregnancy.

Screening tests can involve:

●Blood tests – This involves taking a small amount of your blood for testing in a lab.

●Ultrasound – This is an imaging test that creates pictures of your baby inside your body.

●Both blood tests and ultrasound

Having a screening test does not increase your chance of having a miscarriage. (A miscarriage is when a pregnancy ends on its own before 20 weeks.)

If a screening test shows that there is a high chance that your baby has Down syndrome, you can then choose to have a diagnostic test to find out for sure.

What do the diagnostic tests involve? — Two types of diagnostic tests are available:

●Chorionic villus sampling, also called "CVS" – During CVS, a doctor removes a tiny piece of the placenta. The placenta is the organ that brings the baby nutrients and oxygen and carries away waste. CVS can be done by putting a thin tube through your vagina and into your uterus, or by inserting a needle through your belly. This test is usually done at 11 to 13 weeks of pregnancy.

●Amniocentesis – During amniocentesis, a doctor puts a needle through your belly and uterus and then removes some of the fluid that is around the baby. This test is usually done between 16 and 20 weeks of pregnancy, but it can be done later.

It is important to know that having one of these diagnostic tests gives you a small chance of having a miscarriage because of the test.

How do I decide whether or not to have tests? — This is a personal decision. If you are not sure what to choose, your doctor or nurse can talk to you about the benefits and downsides of the different options. You can also talk with a genetic counselor.

●You might choose a screening test if you want to understand whether your baby has a high or low chance of having Down syndrome. You might feel that you will worry less if there is a low chance that the baby has Down syndrome.

●You might choose a diagnostic test if you want to know for sure if your baby has Down syndrome. You might want the option to have an abortion, or you might want to continue with the pregnancy but have as much information as possible.

●You might choose to have no tests if you feel that "whatever will be, will be." This might be your choice if you know that you would not do anything differently no matter what the test results show.

What happens after my test? — It depends on what kind of test you had.

If you had a screening test that showed that there is a high chance your baby has Down syndrome:

●You might be able to have another, different screening test, which can give you a better idea of how likely your baby is to have Down syndrome.

●You can have a diagnostic test to know for sure if your baby has Down syndrome.

●You can choose to not have any more tests done during pregnancy. You can wait until birth to have a test done to find out if your baby has Down syndrome.

●You can talk to an expert called a "genetic counselor" to help you make a choice.

If you had a diagnostic test that showed that your baby has Down syndrome for sure, your doctor will talk with you about what this means. If you continue with the pregnancy, you might:

●Get extra tests, such as a "fetal echocardiogram" – This test uses sound waves to create a picture of the baby's heart as it beats.

●Choose to give birth in a hospital that has experience caring for babies with Down syndrome.

●Learn more about Down syndrome – This can help give you an idea of what to expect in the future.

More on this topic

Patient education: Down syndrome (The Basics)
Patient education: Amniocentesis (The Basics)
Patient education: Chorionic villus sampling (The Basics)
Patient education: Prenatal care (The Basics)

Patient education: Should I have a screening test for Down syndrome during pregnancy? (Beyond the Basics)
Patient education: Down syndrome (Beyond the Basics)
Patient education: Chorionic villus sampling (Beyond the Basics)
Patient education: Amniocentesis (Beyond the Basics)