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Everything You Want to Know About Noninvasive Prenatal Testing

There are a lot of choices for prenatal testing before your baby is born. One of the newer choices is noninvasive prenatal testing, sometimes abbreviated NIPT. Since NIPT was invented by Dr. Dennis Lo in 2011, more than 6 million pregnant people have received the screening. In this post, we’ll discuss what NIPT is, how it works, and what it can tell you about your baby.

What is NIPT? 

Amniocentesis is a diagnostic-type test—it can reveal more certainty about whether a fetus has a genetic disorder. In contrast, NIPT is a screening test, meaning it can’t give a definitive diagnosis. Instead, NIPT points to the likelihood of a baby being born with a particular genetic condition.

How does NIPT work? 

During pregnancy, small amounts of fetal DNA can be found circulating in the pregnant person’s bloodstream. (In fact, some of that DNA can be found for years after pregnancy in an occurrence called microchimerism.) It’s that circulating DNA that is the basis of the science behind NIPT.

The amount of fetal DNA that is hanging out in maternal blood changes throughout pregnancy, but peaks at between 10 and 20 percent around the late first and early second trimester, which is why the most common timing for NIPT is around weeks 10 to 12. [1] Sometimes as early as 8 weeks or as late as 16 weeks, but at about this point of pregnancy, if you’ve opted to receive an NIPT screening test, you’ll give a blood sample that has to be 10 milliliters or about two teaspoons. The lab technician will then extract the maternal and fetal DNA from the blood and perform sequencing—a technique that allows them to get information about the order of the building blocks that make up DNA.

What can NIPT tell me about my baby?

Based on the sequencing results, NIPT can reveal information about the sex of your baby and whether or not there is an increased chance of aneuploidies, where there is a problem with the number of chromosomes (too many or too few). Typically developing fetuses usually have two of each numbered chromosome and either two X chromosomes or an X and a Y sex chromosome. The genetic risks most commonly identified by NIPT are trisomies (where there are three of a numbered chromosome instead of two) and abnormal numbers of sex chromosomes (for instance, two X chromosomes and a Y or one X chromosome). A risk of trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), and trisomy 21 (Down syndrome) are the trisomies that are most commonly identified as risks during NIPT.

What can NIPT not tell me about my baby? 

NIPT can’t tell you for sure that your baby has an aneuploidy of some kind, so if your screening results indicate that you may have an increased risk for one of the genetic disorders, you’ll likely be referred for amniocentesis. You don’t have to have an amniocentesis, and it can increase the risk for a miscarriage, so if the outcome of the amniocentesis wouldn’t change how you proceed with your pregnancy, then you might want to skip it. It’s always possible to refuse any test or procedure that you’re offered. It’s your body, your pregnancy, and your baby.

Another thing to think about is what the results of the test mean. Typically, something identified on the NIPT is reported as a high or low risk. While it’s unlikely for a noninvasive genetic test to give a false positive for Turner, Down, or Edwards syndromes, there is more room for error in rarer syndromes that involve a smaller portion of the genome, such as DiGeorge Syndrome where a portion of the twenty second chromosome is missing. [2] If you have NIPT results that are confusing or concerning to you, speak to your prenatal provider, and if possible to a genetic counselor. Genetic counselors have specialized education in interpreting NIPT results and helping you understand them.

References

  1. Taglauer, E S et al. “Review: cell-free fetal DNA in the maternal circulation as an indication of placental health and disease.” Placenta, 2014. doi:10.1016/j.placenta.2013.11.014
  2. Macron, A. & Ravitsky V. “Non-invasive prenatal testing: Online discussions show risk perception is highly personal,” The Conversation,
Abby Olena
Dr. Abby Olena has a PhD in Biological Sciences from Vanderbilt University. She lives with her husband and children in North Carolina, where she writes about science and parenting, produces a conversational podcast, and teaches prenatal yoga.

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