Cell-free DNA screening
for trisomy 13, 18 and 21

Healthcare Professional Space

The usual time to result is 5 to 15 working days after reception of the sample by Laboratoire CERBA.
Yet, in about 1 to 2 % of the cases, the result cannot be obtained, thus leading to delayed diagnosis or patient management. It may be the case if the proportion of circulating fetal DNA is too low, especially if the gestational age is too early (lower than 10 weeks of amenorrhea), if the body mass index (BMI) of the patient is higher or in case of placental diseases. In this case, the patient will be proposed to either perform the test again or to go immediately for an invasive procedure.

The sensitivity of the test is greater than 99% for trisomies 13, 18 and 21 but a negative result does not strictly exclude the absence of the abnormalities screened. As a consequence, the sonographic monitoring of the pregnancy must remain unchanged since the morphological ultrasound scan at 2nd and 3rd trimester can also detect signs of other pathologies.

A positive result does not strictly mean that the fetus is affected by one of the abnormalities screened. This is not a test with a definitive diagnosis. Therefore, it is recommended that the patient receive consultation to be informed about:

  • the possibility of a false positive result (0.1 to 0.4 % for this test). 
  • the necessity, in this case, of having a confirmation test after amniocentesis or biopsy of chorionic villi.

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