What noninvasive prenatal testing can (and can’t) tell you about your baby
June 6, 2023
Waiting for the results of a health screening can be stressful; minutes can feel like hours, especially during your pregnancy.
Noninvasive prenatal testing (NIPT) results, in particular, can sometimes trigger heightened concerns because the screening helps determine a baby’s risk of being born with certain chromosomal disorders.
Federal guidelines have made it standard for patients to get immediate access to their health information, which can be a good thing. But lab documents are written for providers, so if a patient looks at NIPT results in their online health portal and sees a phrase like “low fetal fraction” with little or no context, panic may set in. Or, at the very least, they will start looking for answers from Dr. Google.
The best bet is to take a breath and talk with your health care provider or a genetic counselor
to understand what the results may – or may not – mean for your baby. Terms that may sound alarming may not actually be indicative of a problem in your pregnancy.
What does NIPT show?
NIPT has been available for a decade. It initially was used for pregnant patients who were at increased risk of having a baby with a chromosomal abnormality such as Down syndrome, due to maternal age or having a previous baby with a condition. Now, the American College of Obstetricians and Gynecologists (ACOG) recommends that NIPT be offered during every pregnancy to give patients and their providers more information.
NIPT is a genetic screening, not a diagnostic test. Unlike genetic tests that can be done during pregnancy such as amniocentesis or chorionic villus sampling (CVS), NIPT can’t diagnose a condition. It only tells us whether there is a chance a condition exists.
NIPT, also known as cell-free fetal DNA (cffDNA) screening, analyzes small fragments of fetal DNA that circulate in a pregnant person’s blood. What we call “fetal DNA” actually comes from the placenta. NIPT can be done as early as 10 weeks of pregnancy. There usually isn’t enough fetal DNA in the maternal blood before that.
NIPT is noninvasive because it only requires a maternal blood draw and does not disturb the amniotic fluid or placenta. Not all NIPT panels screen for the same things, so ask your health care provider what yours covers. Typically, NIPT can identify whether there is a chance the baby might have:
- Down syndrome (trisomy 21)
- Edwards syndrome (trisomy 18)
- Patau syndrome (trisomy 13)
- Disorders affecting sex chromosomes (X and Y), such as Turner syndrome and Klinefelter syndrome
NIPT can also determine the expected sex of the baby, so if you don’t want to know, indicate that to your doctor or nurse ahead of time. Getting NIPT is optional and is a personal decision. You may also want to contact your insurance company to confirm whether they cover it and what the out-of-pocket costs might be.
While NIPT is very accurate, it can return false negative or false positive results. And because the test analyzes DNA from both the mother and baby, it may detect a genetic condition in the mother she didn’t know she had. The experts in UT Southwestern’s preconception and prenatal genetics service will help you understand the results and plan next steps in managing your pregnancy.
Related reading: 3 questions to ask about Down syndrome testing during pregnancy
"Federal guidelines have made it standard for patients to get immediate access to their health information, which can be a good thing. But lab documents are written for providers, so if a patient looks at NIPT results in their online health portal and sees a phrase like 'low fetal fraction' with little or no context, panic may set in. Or they will start looking for answers from Dr. Google."
What do some common NIPT results mean?
Typically, you get results from your NIPT in about 7-10 days. Different labs use different terminology, so what you see in your results may differ slightly from these examples:
Negative or low risk: This is the most common result, and it means the test showed the expected amount of chromosomal material coming from the pregnancy, suggesting there is low risk for the specific abnormalities listed. This is not a guarantee the baby doesn’t have a condition, but the risk is low.
Positive or high risk: This result suggests a possible chromosomal abnormality in the pregnancy. Depending on the chromosome involved, there is a variable chance of a false positive. Positive results can also be indicative of a chromosome abnormality isolated to the placenta (not in the fetus), or in some cases a maternal chromosome abnormality. When you get a positive or high-risk result, you’ll also get a positive predictive value, or PPV.
Positive predictive value: This is the probability that a positive test result is truly positive. Many factors go into this number, including the sensitivity of that specific test, the incidence of the noted condition, and maternal age. For example, NIPT is the most accurate in screening for Down syndrome, so the PPV usually will be higher for Down syndrome than for some other conditions. And the PPV of a positive Down syndrome screening result may be higher for a mom who is 40 versus a mom who is 30.
Low fetal fraction or insufficient fetal DNA: These terms may sound scary, but they only mean there weren’t enough placental chromosome fragments in the blood sample to run the test – often because it’s too early in the pregnancy. Other factors can include obesity or overweight, certain autoimmune conditions, or some medications such as blood thinners. Specific chromosome abnormalities including trisomy 13, trisomy 18, and triploidy have been associated with a low fetal fraction, however the risk for these rare conditions with a low fetal fraction result is still low.
Atypical findings: This is a rare test result that indicates a suspected abnormality outside the more common disorders for which NIPT screens. A genetic counselor can help clarify what these results might be indicating.
Peek into your genetic compatibility with carrier screening
Carrier screening estimates the chances a child you have with your partner might inherit a genetic condition, such as sickle cell disease, cystic fibrosis, or spinal muscular atrophy (SMA).
What if NIPT results indicate high risk?
If there was low fetal fraction or insufficient fetal DNA, we can try the test again. If you got a result that is positive or high risk for a certain disorder, remember it is not a diagnosis. We need more information for that.
Some parents prefer to wait until their baby is born to get a diagnosis. Others want a definitive answer during the pregnancy. In those cases, the next step would be prenatal genetic testing to diagnose the condition before birth. We offer two prenatal diagnostic tests at UT Southwestern: amniocentesis or chorionic villus sampling (CVS). Both are performed by our maternal-fetal medicine physicians, who specialize in caring for high-risk pregnancies and performing minimally invasive procedures during pregnancy.
Every pregnancy is different. So is every family. But try not to draw conclusions before you can review the test results with your provider. We will give you the complete picture and help you make the best choice for you and your pregnancy.
To discuss noninvasive prenatal testing with a genetic counselor, call 214-645-8300 or request an appointment online.
