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Prenatal Cell-Free DNA Screening
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Prenatal Cell-Free DNA Screening

Prenatal cell-free DNA (cfDNA) screening is a non-invasive blood test that assesses the risk of certain chromosomal conditions in a developing fetus.

What is a prenatal cell-free DNA (cfDNA) screening?

Prenatal cell-free DNA (cfDNA) screening is a blood test given during pregnancy. During pregnancy, some of the fetus's DNA circulates in the mother's bloodstream. A cfDNA screening checks this DNA to find out if the baby is more likely to have certain conditions caused by an abnormal number of chromosomes, such as Down syndrome.

Chromosomes are tiny "packages" in your cells that contain your genes. Genes carry information, called DNA, that controls what you look like and how your body works.

  • Normally, you're born with a set of 46 chromosomes in each cell. The chromosomes are grouped into 23 pairs. Each pair has two chromosomes, one coming from each parent.
  • If one of these pairs has an extra copy of a chromosome, it's called a trisomy. A trisomy causes changes in the way the body and brain develop.
  • If there is an extra copy of chromosome 21, it's called Down syndrome (trisomy 21). This is the most common chromosome disorder in the United States.
  • Other trisomy disorders include Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13). These disorders are rare but more serious than Down syndrome. Most babies with trisomy 18 or trisomy 13 die within the first year of life.

There is very little risk to you and your baby with a cfDNA screening. However, a cfDNA screening can't tell you for sure whether your baby has a chromosome disorder. Your health care provider will need to order other tests to confirm or rule out a diagnosis.

Other names: cell-free fetal DNA, cffDNA, non-invasive prenatal test, NIPT, non-invasive prenatal screening, NIPS.

What is it used for?

A cfDNA screening is most often used to show if your unborn baby has an increased risk for Down syndrome, Edwards syndrome, or Patau syndrome. It may also be used to:

  • Determine a baby's sex. This may be done if an ultrasound shows that a baby's genitals are not clearly male or female, which may be caused by a disorder of the sex chromosomes.
  • Check Rh blood type. If you are Rh negative and your unborn baby is Rh positive, your body's immune system may attack your baby's blood cells. If you find out you are Rh negative early in pregnancy, you can take medicines to protect your baby from dangerous complications.

A cfDNA screening can be done as early as the 10th week of pregnancy.

Why do I need a prenatal cfDNA screening?

Many providers recommend this screening if you are pregnant and are at a higher risk of having a baby with a chromosome disorder, such as:

  • You are age 35 or older.
  • You've had another baby with a chromosome disorder.
  • Your fetal ultrasound didn't look normal.
  • Other prenatal test results were not normal.

Many providers recommend screening even if you aren't at higher risk, as the screening has almost no risk and a high rate of accuracy.

What happens during a prenatal cfDNA screening?

A health care professional will take a blood sample from a vein in your arm using a small needle. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

What do the results mean?

If your results were negative, it's unlikely that your baby has Down syndrome or another trisomy disorder.

If your results were positive, it means there is an increased risk that your baby has one of these disorders. To confirm a diagnosis, you'll need other tests, such as:

  • Amniocentesis. This test takes a sample of the amniotic fluid that surrounds the unborn baby in the uterus. It is usually done between weeks 15 and 20 of pregnancy.
  • Chorionic villus sampling (CVS). This collects tissue from the placenta. It may be done between weeks 10 and 13 of pregnancy.

These tests are usually very safe, but they do have a slight risk of causing a miscarriage.

Is there anything else I need to know?

cfDNA screenings are not as accurate if you are pregnant with more than one baby (twins, triplets, or more).

Frequently Asked Questions

"no-call" result occurs when there is not enough fetal DNA in the sample to provide a reliable risk assessment. This is not a diagnosis of a problem but rather a technical limitation of the sample. If this happens, your provider may recommend repeating the blood test in a few weeks to allow more fetal DNA to circulate, or they may suggest alternative diagnostic methods such as amniocentesis or chorionic villus sampling (CVS) to obtain a definitive answer.
positive cfDNA result indicates a high risk that the fetus has a specific chromosomal condition, such as Down syndrome, but it is not a definitive diagnosis. Because the test analyzes cell-free DNA fragments in the mother's blood, it is a screening tool rather than a diagnostic one. To confirm the result, invasive diagnostic tests like amniocentesis or CVS are required, which involve sampling amniotic fluid or placental tissue. These procedures carry a small risk of miscarriage but provide a 100% accurate diagnosis.
The most accurate results are typically obtained when the test is performed after 10 weeks of pregnancy. Testing before this window may result in insufficient fetal DNA in the maternal bloodstream, which can lead to a "no-call" result where the lab cannot provide a definitive risk assessment. Your healthcare provider will usually schedule the blood draw between 10 and 22 weeks, though it can be performed later in pregnancy if needed.
Yes, several maternal factors can influence the accuracy of the test. Conditions such as a higher body mass index (BMI), recent organ transplantation, or certain blood disorders can alter the proportion of fetal DNA in the blood or interfere with the analysis. Additionally, if the mother has a chromosomal abnormality herself, the test may reflect her genetic makeup rather than the fetus's. It is important to discuss any underlying health conditions with your provider before testing to interpret the results correctly.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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