Non-Invasive Prenatal Testing on the Rise
When I was pregnant with my son and second child at age 36, the health of my baby weighed heavily on me. My first child was healthy, but the risk of Down syndrome shoots upward at age 35, and by age 40 it climbs to 1 in 100. Standard screening tests — a combination of blood tests and an ultrasound to measure fluid at the back of the neck — might have set my mind at ease. On the other hand, a low-risk result wouldn’t mean my baby was free of Down syndrome, and a high-risk result more than likely wouldn’t mean he wasn’t.
Down syndrome isn’t the only or most severe condition that might worry parents-to-be — only the most common. If I really needed to know all I could with greater certainty, it would mean amniocentesis or chorionic villi sampling (CVS), in which finger-like growths from the placenta are removed to determine chromosomal or genetic disorders in the fetus. But those invasive procedures come with a risk of miscarriage. Low as that risk may be, it wasn’t something I wanted to consider. I opted out for fear, in my case, that they could only increase my anxiety. That wouldn’t be the right choice for everyone, of course, but it was for me.
Expectant moms now have a new option: non-invasive prenatal testing, or NIPT. It’s based on cell-free fetal DNA — genetic material derived from the placenta that circulates in a pregnant mother’s blood stream. With a simple blood draw, that DNA can be isolated and analyzed for common genetic abnormalities by one of four U.S. companies: Sequenom Laboratories, Natera, Verinata Health and Ariosa Diagnostics.
Dr. Neeta Vora, a physician and assistant professor in UNC-Chapel Hill’s Department of Obstetrics and Gynecology, as well as director of the Maternal Serum Screen Laboratory, says NIPT has a better detection rate and lower incidence of false positives than standard screening tests do. Studies suggest it is very good in detecting Down syndrome (also known as trisomy 21), along with trisomies 13 and 18, which are less common but more severe conditions. In a study of more than 200 pregnant women that Vora published in Genetics in Medicine, the official journal of the American College of Medical Genetics and Genomics, the test didn’t perform quite as well in clinical practice as the bigger industry-sponsored studies show. Still, it is less likely, compared to standard serum testing, to suggest a problem where one doesn’t exist. Vora has seen more and more women opting for NIPT every month and fewer undergoing amniocentesis as a result.
So far, NIPT is only recommended for women considered “high-risk” based on advanced maternal age, ultrasound findings or family history of a trisomy. NIPT can also be used following a positive first- or second-trimester screening. It’s important to note that any positive NIPT result should still be confirmed by amniocentesis or CVS.
Experts say eventually NIPT may be offered to all women, perhaps allowing the new test to replace other early screening tests entirely. It’s likely that companies will add to the results they offer, too. In fact, two companies already offer an optional panel of rare microdeletions (tiny pieces from a chromosome that are too small to be readily seen through a microscope). Because those tests aren’t well validated yet, Vora recommends exercising caution for now.
As with any genetic test, it’s always a good idea to talk with a genetic counselor first. And remember, these decisions will always be personal, just as mine was for me.
“It’s important that couples understand the sensitivity, false positive rate and what kind of information they’ll get,” Vora said. “Every couple is different in terms of what they want to know.”
Kendall K. Morgan, Ph.D., is a science writer and grateful mother of two healthy children. She lives in Durham with her family, dog, two cats, four hermit crabs and flock of chickens.