Down Syndrome Tests
Reviewed
Also called: Down syndrome tests, Trisomy 21 tests, prenatal screening for Down syndrome, diagnostic tests for Down syndrome
Down syndrome tests are used during and after pregnancy to check for an extra copy or piece of chromosome 21. Screening tests (blood tests, ultrasound, cell-free DNA) estimate the chance that a fetus has Down syndrome. Diagnostic tests (amniocentesis, CVS, PUBS, newborn karyotype) can confirm whether Down syndrome is present. Screening is recommended for all pregnant individuals, and diagnostic testing is offered to those with higher risk or after a positive screening. Results from screening tests are reported as screen-positive (higher likelihood) or screen-negative (lower likelihood). Diagnostic test results confirm whether Down syndrome is present but cannot predict the severity of its effects.
Specimen: Specimen type depends on the test: maternal blood, amniotic fluid, chorionic villi, umbilical cord blood, or newborn blood.
Why this test may be ordered
- To estimate the chance that a fetus has Down syndrome (screening tests).
- To confirm whether a fetus or newborn has Down syndrome (diagnostic tests).
- Recommended for all pregnant individuals regardless of age or risk (screening).
- Offered to those with higher risk: age 35 or older, previous child with Down syndrome, family history, or ultrasound findings suggestive of Down syndrome.
Preparation and collection
Preparation varies by test. Blood tests and ultrasounds usually require no preparation. For amniocentesis or CVS, you may need to drink extra fluid and not urinate before the test to keep your bladder full. For PUBS after 23 weeks, you may need to fast for several hours. No preparation is needed for a newborn karyotype test.
See specific test descriptions
Risks vary by test type. Blood tests and ultrasounds have very little risk (minor pain or bruising). Amniocentesis and CVS may cause mild stinging or cramping and have a slight risk of miscarriage. PUBS has a slightly higher risk of serious complications. Newborn karyotype testing has no risk. Always discuss risks with your provider.
Understanding results
The interpretation of test results should be provided by your healthcare professional. Below are general patterns based on the type of test.
- Screen-positive (higher likelihood): Your baby's chance of having Down syndrome is higher than average. Limitation: Screening tests cannot diagnose Down syndrome; they only estimate risk. Next step: If you receive a screen-positive result, you may choose to have a diagnostic test for confirmation. A genetic counselor can help you decide.
- Screen-negative (lower likelihood): Your baby is unlikely to have Down syndrome based on the screening. Limitation: A negative screening result does not guarantee that your baby will not have Down syndrome. Next step: If you still have concerns, you may discuss diagnostic testing or further screening options with your provider.
- Screening tests only estimate the chance of Down syndrome; they cannot diagnose the condition.
- A negative screening result does not guarantee that the baby will not have Down syndrome.
- Diagnostic tests confirm whether Down syndrome is present but cannot predict the severity of its effects on health and abilities.
- Diagnostic tests (amniocentesis, CVS, PUBS) carry a small risk of miscarriage or other complications.
What to do next
If you have questions about your results, speak with a healthcare provider or genetic counselor. They can help you understand the risks and benefits of testing and what your results mean for your pregnancy or child.
- What do my screening test results mean for my baby's chance of having Down syndrome?
- Should I consider a diagnostic test after a positive screening result?
- What are the risks and benefits of diagnostic testing?
- How will a diagnosis of Down syndrome affect my baby's health and development?
- Can a genetic counselor help me understand my options?