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Test Overview
Cell-free fetal DNA is an optional screening test to look for certain conditions in a fetus. It can tell you if there is a high or low chance for genetic conditions caused by an abnormal number of chromosomes. This test can also predict the sex of the fetus.
This is a blood test for the pregnant person. The test can be done as early as 10 weeks in the pregnancy.
If this screening test is positive, it means there is a chance your baby has genetic condition. In that case, your clinician may offer you a diagnostic test, which can show if the condition is present.
Sometimes the test does not give a result. If the test does not give a result, you may be asked to come back and take the test a second time.
Why It Is Done
The test is done to look for certain genetic conditions caused by too many or too few chromosomes. This test only screens for the conditions listed below. It does not screen for all genetic conditions. It also does not look for any other type of birth defects.
- This test can find trisomy 21 (Down syndrome) 99 times out of 100 (99%).
- This test can find trisomy 18 (Edward syndrome) 95 times out of 100 (95%).
- This test can find trisomy 13 (Patau syndrome) 94 times out of 100 (94%).
If you are carrying one baby, the test will also look for X and Y chromosome variations including:
- Turner syndrome
- Klinefelter syndrome (XXY)
- Trisomy X
- XYY
This test may also screen for other chromosomal birth defects. Check with your clinician to find out if any other conditions are included.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm. You do not need to do anything to prepare for the test.
Results
A negative result means that your baby is unlikely to have one of the conditions this test looks for.
A positive result means that your baby may have a genetic condition. More testing is needed to be sure. No decision about the pregnancy should be made only on a positive (abnormal) result.
An inadequate result means that the test was not able to be completed. This can happen if the test does not meet all the quality control checks at the lab. A second (repeat) test will sometimes give a result.
An inconclusive result means that variations of the X and Y chromosomes could not be determined.
A screening test is not 100% accurate.
- Cell-free DNA screening can give false positive results. This is when the test shows a positive result in a healthy pregnancy.
- Cell-free DNA screening can also give false negative results. This is when the test shows a negative result when a fetus has one of the conditions being screened. This is rare.