In plain words
Cell-free DNA screening is a blood test offered in pregnancy. Small pieces of DNA from the placenta move freely in the mother's blood. The test reads them to estimate the chance of certain chromosome conditions, most often Down syndrome, trisomy 18, and trisomy 13. It can also estimate the baby's sex. The test is a screen. A higher-risk result usually leads to a diagnostic test, such as or , to confirm. A lower-risk result is reassuring, but it does not rule out every condition. How often a positive result is correct depends on how common the condition is in the group being tested. That is why age and other factors matter. Many people are offered this test, and whether to take it is a personal choice.
The deeper version
Cell-free DNA screening sequences placenta-derived cfDNA in maternal plasma to estimate the risk of in chromosomes 21, 18, and 13, and of sex chromosome abnormalities. Published screening studies report detection rates above 99 percent for trisomy 21 (ACOG Practice Bulletin No. 226, 2020). depends on pretest probability, so the same performance yields more false positives at low prior risk. ACOG recommends that all pregnant patients be offered aneuploidy screening and diagnostic testing regardless of age. Limitations include test failure, vanishing twin effects, and confined placental mosaicism, and performance for rarer conditions is lower. Chorionic villus sampling or amniocentesis remains the diagnostic reference standard. Debate continues over expansion to microdeletions and over consent for broader panels.
Where it comes up
- Pregnancy at 35 and olderPregnancy: Your Body
- Prenatal tests and ultrasounds: what each one isPregnancy: Your Body
- Termination for medical reasonsLoss and Complications
- Expecting twins or morePregnancy: Your Body
What mothers here say about cell-free DNA screening
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Sources
- American College of Obstetricians and Gynecologists — Practice Bulletin No. 226: Screening for Fetal Chromosomal Abnormalities, 2020
- American College of Obstetricians and Gynecologists — Committee Opinion No. 640: Cell-Free DNA Screening for Fetal Aneuploidy, 2016