Down Syndrome Tests
Reviewed
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.
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.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- 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.