Understanding Noninvasive Prenatal Testing

Woman having blood drawn
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Noninvasive Prenatal Testing (NIPT) is a way to screen for some genetic disorders by looking at the mother's blood. You may also hear it called noninvasive prenatal screening (NIPS). These are the same thing. These test work by finding a small amount of the baby's DNA that circulates in the mother's blood stream, known as cell free DNA or cfDNA. The blood is drawn in the same way as any other lab work is drawn and sent to a lab to screen for a variety of genetic disorders.

There are a few tests offered—which test you are offered will depend on the lab that your practitioner typically uses. Some of the test names include:

  • Harmony
  • MaterniT21 Plus
  • VisabiliT
  • Panaorama
  • Verifi 

Who Should Do NIPT?

The American College of Obstetricians and Gynecologists (ACOG) now recommends genetic testing by either screening (NIPT) or diagnostic testing (amniocentesis or chorionic villus sampling), for every pregnant woman.

If your doctor recommends screening for you, don't get worried. It's not necessarily because he or she suspects something is wrong. Traditionally, these types of tests and screenings were recommended only for women who were over the age of thirty-five or who had a family history of a genetic disorder. The recommendation then expanded to include older fathers. Now the screenings are safer and more readily available, so they are more widely recommended.

One thing that some families do not think about beforehand is what will happen if the test is positive, indicating that your pregnancy is at an increased risk for a genetic problem.

This is certainly a discussion we would encourage you to have with your practitioner and your partner. One thing that is important to remember is that these tests are considered a screening test, meaning that they can only tell you about an increased risk of your baby having a genetic issue, not necessarily the definite presence of genetic issues.​ You would need to have a diagnostic test for a definitive answer about your baby's genetic status.

Note that if you are obese or morbidly obese, there is an increased risk that the test will not work for you, meaning no result is given. This means that this might not be the best screening for you if you are over two hundred and fifty pounds. NIPT may also have limitations if you are pregnant with twins or other multiples.

When Do you Do NIPT?

You can begin to use NIPT tests as early as the ninth week of your pregnancy. Ideally, this discussion would take place as early as possible in pregnancy, including your first prenatal visit. This timing gives you more time to discuss what your options for screening are based on your medical and familial history, as well as a chance to take advantage of first trimester screening opportunities, like the nuchal fold testing with ultrasound.

What Does NIPT Screen For?

These screenings look for only the most common genetic disorders. Note that with there being multiple different brands of NIPT available, each one may have a slightly different panel of what it is looking for in the lab.

Here is what is most likely included in the test:

There are also other things that some NIPTs will tell you. This can include your baby's Rh status, the sex of your baby, etc. Though these may vary depending on the test that your practitioner uses.

How Accurate Is NIPT?

If you were to look at the advertisements for and individual laboratory doing a specific test, they usually quote very high rates of accuracy. This is misleading for most people because the testing done to look at the accuracy was done in a population with a higher rate of genetic problems. This means it may not be as relatable to a general population of pregnant women. We are also not able to tell you how likely your baby is to truly have a genetic problem if you have a positive screening test.

What Comes After NIPT?

If you have a NIPT test that comes back indicating that your baby may have a genetic problem, you will be counseled. This counseling will usually involve a discussion at length with a genetic counselor going over your personal and medical history and explaining what other tests are available. Early in pregnancy, the chorionic villus sampling (CVS) is used and after fourteen weeks gestation, you can also do amniocentesis. 

These are considered diagnostic tests rather than screening tests. This means that they will actually provide a diagnosis rather than simply indicate what your risk is for having a baby who has a genetic problem. These tests are more accurate, but also come with a slight risk to the pregnancy. With an experienced provider, the risk of a miscarriage after these tests is 0.1 to 0.3 percent according to ACOG. This risk is independent of the diagnosis of a genetic anomaly.

Other Genetic Testing

It is important to note that NIPT does not screen for neural tube defects like spina bifida or anencephaly. Therefore second trimester screenings with ultrasound and/or maternal serum alpha feto-protein (MSAFP) should still be offered to parents. Some parents may also opt to skip genetic screening tests, preferring to go straight to the diagnostic tests, for a variety of reasons. Talking to your doctor or midwife about your preferences, your medical history, and other factors including what you would or would not do if you receive a diagnosis of a genetic disorder, will help you have a conversation and choose the right path for you and your family.

Opting for No Genetic Testing

Some families will also make the decision to skip the genetic testing, whether that is a screening test or a diagnostic test. Your practitioner should not try to force you into making another choice, but a discussion should be had about the benefits and risks of all of the options. ACOG, the American Academy of Nurse Midwives (ACNM), and other medical organizations all support your right to refuse genetic screening and testing.

Sources:

Allyse M, Minear MA, Berson E, Sridhar S, Rote M, Hung A, Chandrasekharan S. Non-invasive prenatal testing: a review of international implementation and challenges. Int J Womens Health. 2015; 7: 113–126. Published online 2015 Jan 16. doi:  10.2147/IJWH.S67124.

American College of Obstetricians and Gynecologists Committee on Genetics and the Society for Maternal-Fetal Medicine. Committee Opinion No. 640: Cell-free DNA screening for fetal aneuploidy. Obstetrics & Gynecology. 2015;126:e31.

Gregg AR, Gross SJ, Best RG, Monaghan KG, Bajaj K, Skotko BG, Thompson BH, Watson MS. American College of Medical Genetics and Genomics.ACMG statement on noninvasive prenatal screening for fetal aneuploidy. Genet Med 15: 395-398; advance online publication, April 4, 2013; doi:10.1038/gim.2013.29

Society for Maternal-Fetal Medicine Publications Committee. #36: Prenatal aneuploidy screening using cell-free DNA. American Journal of Obstetrics and Gynecology. 2015;212:711.

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