Testing & Diagnosis for Down Syndrome in Children

Receiving a diagnosis of Down syndrome can be a stressful time for your family. You are being given a lot of new information and you probably have a long list of questions. All of the members of our team in the Boston Children’s Hospital Down Syndrome Program are here to help.

How is Down syndrome diagnosed?

Down syndrome can be detected during pregnancy through prenatal tests. Down syndrome can also be diagnosed after birth with a chromosomal analysis called a karyotype.

Why are prenatal tests used?

Prenatal tests are optional tests that can be performed during pregnancy to identify a fetus’s sex, age, size and placement in the uterus. Prenatal tests also detect chromosomal conditions, congenital heart defects, and other genetic conditions.

How early should parents consider prenatal testing?

Ideally, the best time to start thinking about prenatal tests is before conception. Although no testing can be done at that point, the doctor can look at your family’s medical history to see if you might have an increased risk for genetic conditions such as Down syndrome.

The American College of Obstetrics and Gynecologists now recommends that all women be offered prenatal testing.

What are the different types of prenatal tests?

Before any parent decides whether or not to get prenatal testing, it’s important to know all the options and the advantages and disadvantages of each one. The two types of prenatal tests used to detect Down syndrome are called screening tests and diagnostic tests.

Screening tests

  • Screening tests determine the likelihood of Down syndrome or other medical conditions. This kind of testing does not definitively diagnose a fetus with one of these conditions.

The different types of screening tests include:

  • blood tests, which are used to measure protein and hormone levels in pregnant women. Abnormally increased or decreased levels can indicate a genetic condition.
  • ultrasound, which is a non-invasive imagining technique that uses sound waves to generate an image of the fetus. An ultrasound can identify congenital heart conditions and other structural changes such as extra skin at the base of the neck that may indicate a diagnosis of Down syndrome.

The combined results of blood test and ultrasound results are used to estimate the chance that the fetus has Down syndrome.

If there is a high probability result on those screening tests or if there is a higher chance of Down syndrome due to maternal age, newer tests (such as MaternaT21 or Panorama) look for fetal DNA in the maternal blood and can let you know if there is a very high probability (>99%) or very low probability (<1%) that the fetus has Down syndrome. However, these tests are not diagnostic and cannot tell you with certainty whether or not the fetus has Down syndrome.

Diagnostic tests

  • Diagnostic tests can determine whether or not your fetus has Down syndrome with nearly 100 percent accuracy. However, because these tests require using a needle to obtain a sample from within the uterus, they carry a small increased risk of miscarriage and other complications.

The different types of diagnostic testing include:

  • Chorionic villus sampling (CVS), a prenatal diagnosis method in which a small biopsy of the placenta is taken for specific genetic testing. CVS is used to detect any condition that involves specific chromosomal abnormalities, like Down syndrome. This test is usually performed during the first trimester between 10-14 weeks of gestation.
  • Amniocentesis, a prenatal diagnosis method in which a needle is inserted into the amniotic sac that surrounds the baby. Amniocentesis is most often used to detect Down syndrome and other chromosomal abnormalities. This test is usually done in the second trimester, after 15 weeks of gestation.

Prenatal testing for associated conditions:

  • Ultrasound: In addition to screening for markers suggestive of a diagnosis of Down syndrome, ultrasound can be used to diagnose co-existing problems such as blockage in the intestine.
  • Prenatal cardiac echo: Boston Children’s Hospital cardiologists can perform and interpret fetal echocardiograms providing information on congenital heart defects.
  • Fetal MRI: An MRI (magnetic resonance imaging) study of the fetus within the uterus of a pregnant woman can be used to gather more detailed information about body structures (such as the brain or the intestines). Fetal MRIs can be performed at Boston Children’s Hospital and interpreted by specialized radiologists in the Advanced Fetal Care Center.

Diagnostic Testing after birth

Down syndrome can also be diagnosed after the baby is born:

  • Since Down syndrome involves a set of unique characteristics, a doctor can usually tell whether a baby should be tested based on a physical examination.
  • To confirm the findings, a rapid blood test (FISH) can be sent to confirm the presence of extra material from chromosome 21. Those results are available within a few days. In addition, blood will be sent for karyotype (which takes about 1-2 weeks for results) . This gives further information on the type of Down syndrome (see above) which is important in determining the chance of trisomy 21 in a future pregnancy.

What should I do if I receive a prenatal diagnosis of Down syndrome?

Our Boston Children’s Hospital Down Syndrome Program works closely with the Advanced Fetal Care Center at Boston Children’s Hospital. We provide prenatal consultation with a physician from our Down Syndrome Program to help you learn more about Down syndrome and answer any questions. These sessions are confidential and family-centered. For families who are uncertain of their plans, we provide non-directive counseling, giving them a safe opportunity to gather the information they need to make an informed decision about their pregnancy.

For families with a likely or confirmed diagnosis who are continuing their pregnancy, the prenatal visit becomes the first clinical visit where we begin to plan for the baby’s future. We discuss common medical conditions, developmental issues, education, and resources in the community.

Whether or not you opt for a visit in the Advanced Fetal Care Center, we welcome you to join the clinic when the baby is born. You are also welcome to contact our Program Coordinator for more information on Down syndrome and about the Boston Children’s Hospital Down Syndrome Program.

What if I receive a diagnosis of Down syndrome after the baby is born?

We realize that an unexpected diagnosis of Down syndrome can leave a family with many questions and concerns and so we are happy to expedite an initial visit for you and your new baby.

At Boston Children's Hospital, we take a family-centered approach to care. From your first visit, you'll work with a team of professionals who are committed to supporting all of your family's physical and psychosocial needs, including putting you in touch with other families with a child who has Down syndrome, and connecting you to community and educational services.