What is a prenatal cell-free DNA (cfDNA) screening?
Prenatal cell-free DNA (cfDNA) screening is a blood test for pregnant women. During pregnancy, some of an unborn baby’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 Down syndrome or another disorder caused by a trisomy.
A trisomy is a disorder of the chromosomes. Chromosomes are the parts of your cells that contain your genes. Genes are parts of DNA passed down from your mother and father. They carry information that determines your unique traits, such as height and eye color.
- People normally have 46 chromosomes, divided into 23 pairs, in each cell.
- 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.
- In Down syndrome, there is an extra copy of chromosome 21. This is also known as trisomy 21. Down syndrome is the most common chromosome disorder in the United States.
- Other trisomy disorders include Edwards syndrome (trisomy 18), where there is an extra copy of chromosome 18, and Patau syndrome (trisomy 13), where there is an extra copy of chromosome 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.
A cfDNA screening has very little risk to you and your baby, but it 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
What is used for?
A cfDNA screening is most often used to show if your unborn baby has an increased risk for one of the following chromosome disorders:
- Down syndrome (trisomy 21)
- Edwards syndrome (trisomy 18)
- Patau syndrome (trisomy 13)
The screening may also be used to:
- Determine a baby’s gender (sex). This may be done if an ultrasound shows that a baby’s genitals are not clearly male or female. This may be caused by a disorder of the sex chromosomes.
- Check Rh blood type. Rh is a protein found on red blood cells. If you have the protein, you are considered Rh positive. If you don’t, you are Rh negative. 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 health care providers recommend this screening to pregnant women who are at higher risk of having a baby with a chromosome disorder. You may be at higher risk if:
- You are age 35 or older. A mother’s age is the primary risk factor for having a baby with Down syndrome or other trisomy disorders. The risk increases as a woman gets older.
- You’ve had another baby with a chromosome disorder.
- Your fetal ultrasound didn’t look normal.
- Other prenatal test results were not normal.
Some health care providers recommend screening to all pregnant women. This is because the screening has almost no risk and has a high rate of accuracy compared with other prenatal screening tests.
You and your health care provider should discuss if a cfDNA screening is right for you.
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. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for this test?
You may want to speak to a genetic counselor before you get tested. A genetic counselor is a specially trained professional in genetics and genetic testing. He or she can explain the possible results and what they might mean to you and your baby.
Are there any risks to the test?
There is no risk to your unborn baby and very little risk to you. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
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. But it can’t tell you for sure if your baby is affected. For a more confirmed diagnosis you’ll need other tests, such as amniocentesis and chorionic villus sampling (CVS). These tests are usually very safe procedures, but they do have a slight risk of causing a miscarriage.
If you have questions about your results, talk to your health care provider and/or a genetic counselor.
Is there anything else I need to know about a prenatal cfDNA screening?
cfDNA screenings are not as accurate in women who are pregnant with more than one baby (twins, triplets, or more).
Courtesy of MedlinePlus from the National Library of Medicine.