What Is Noninvasive Prenatal Testing?

When you are pregnant, you have so many questions about your baby. Prenatal testing can answer some of those questions. Noninvasive prenatal testing (NIPT) can tell you whether your baby is at risk for certain genetic conditions, such as Down syndrome. It can't tell you for sure whether your baby has one of those conditions. For that reason, some health professionals prefer to use the term noninvasive prenatal screening, or NIPS, rather than NIPT.

If you get a positive result from NIPT and want to confirm that your baby has a particular genetic condition, you'll have to follow up with diagnostic testing. Some parents want as much information as possible before their baby is born. Others do not. Understanding the benefits and limits of NIPT testing can help you decide whether you want it. 

How Is NIPT Done?

We've all heard about DNA and how it carries the genetic information for humans and other living creatures. You may know that DNA is a part of every human cell. Tiny bits of DNA also circulate in the blood. Those bits are called cell-free DNA, or cfDNA. When you are pregnant, your blood also carries bits of your baby's DNA, called cell-free fetal DNA, or cffDNA.

 Scientists can take a sample of your blood and examine the DNA in it for evidence of certain genetic conditions. Because NIPT consists of a simple blood test, it doesn't create a risk for you or your baby.

What Can NIPT Tell You?

NIPT is most often used to screen for trisomy. Normal chromosomes come in pairs. When a baby has three copies of a particular chromosome, the condition is classified as a trisomy.

The most common trisomy in newborns is Down syndrome or trisomy 21. NIPT usually checks for it and also for Patau syndrome (trisomy 13) and Edward syndrome (trisomy 18). It can also screen for certain abnormalities in the sex chromosomes.

NIPT is quite accurate for Down syndrome (99%) and for trisomy 18 (97%). It is less accurate for trisomy 13 (87%). In all cases, the results should not be considered certain unless confirmed by diagnostic testing. 

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Two diagnostic procedures can usually confirm or disprove the results of NIPT. The results can be confirmed with amniocentesis, which involves sampling the fluid inside the uterus. They can also be confirmed with chorionic villus sampling(CVS), which tests cells taken from the placenta. Both of these procedures are considered invasive and carry some risks. Some mothers opt not to use them.

Some companies offering NIPT also test for certain microdeletions, which are conditions caused by chromosomes that are missing a section. NIPT is less accurate in screening for microdeletions than in screening for trisomy. Tests for microdeletions have a high rate of false positives. For that reason, many parents opt out of these tests even when they are offered.

NIPT will also show the baby's sex. You will need to let your doctor know if you do not want to know that information.

No screening or testing procedure can guarantee that your baby will have no health problems. NIPT doesn't screen for many conditions that can affect your baby. Your doctor will advise you about other available tests and screening procedures. 

Who Should Have NIPT?

Noninvasive prenatal testing is available to all mothers after they have been pregnant for at least 10 weeks. No one is required to undergo it. Mothers who are at an increased risk of certain genetic disorders may be more interested in testing. They will also have a lower rate of false positives. 

Women are considered high-risk if they are over 35, if they have already had a child with a trisomy, or if they have received a positive result from a different screening test.

NIPT may not work well for mothers in certain situations. NIPT works by testing all the cell-free DNA circulating in the mother's blood. Most of the DNA comes from the mother. Only 10% to 20% of it comes from the baby. For that reason, NIPT results are based on very small increases in DNA containing a certain chromosome. Many conditions in the mother's body can interfere with getting accurate test results. 

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NIPT may not be reliable for moms who:

If you get a non-conclusive result from NIPT, you may opt for a diagnostic test to determine whether your baby has a genetic condition, or you may pass on further procedures.

Insurance may or may not pay for NIPT, depending upon your policy and possibly on whether you are a high-risk mother.

Next Steps After NIPT

Getting a positive result from NIPT can be upsetting. A genetic counselor can help you understand the results. Remember that NIPT results are not considered reliable unless confirmed by diagnostic testing. You do not have to opt for further testing, but you should not make any important decisions on the basis of a screening test alone. 

WebMD Medical Reference Reviewed by Dan Brennan, MD on March 10, 2021

Sources

SOURCES:

The American College of Obstetricians and Gynecologists: "Cell-Free DNA Prenatal Screening Test."

Australian Family Physician: "Non-invasive prenatal testing."

British Journal of General Practice: "Non-invasive prenatal testing: use of cell-free fetal DNA in Down syndrome screening."

Centre for Genetics Education: "Fact Sheet 27: Non-Invasive Prenatal Testing (NIPT)."

Cleveland Clinic: "Prenatal Testing: Do You Know the Benefits and Limits?"

Mayo Clinic: "Prenatal cell-free DNA screening."

Society for Maternal-Fetal Medicine: "Cell free DNA screening is not a simple blood test."

University of California San Francisco: "FAQ: Cell-Free DNA Screening."

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