Making the rounds on Facebook is news that an Irish couple aborted their preborn child upon receipt of a positive test result for Edwards Syndrome, only to discover afterward that the baby was healthy. Edwards Syndrome causes life-threatening organ defects, an abnormally shaped head, and—if the child survives—developmental delays. It is usually fatal within the first year of a child’s life, often within the first several days after birth.
The couple was told by medical professionals at the National Maternity Hospital that there was “no hope” for their baby, even though some people with Edwards Syndrome have gone on to live joyful lives despite their serious impediments. They were strongly encouraged to take advantage of Ireland’s newly legal abortion framework, and did so at 15 weeks’ gestation.
As Live Action reported, the mother underwent chorionic villus sampling (CVS), in which cells from the placenta are sampled to screen for chromosomal abnormalities. According to reporting by the Irish Times, the test is “99% accurate,” and “in 0.15 per cent of cases, a false positive can occur.” Some may be shocked that a healthy baby could be aborted “by mistake.” A 0.15 percent false positive rate? That’s tiny, right? How could they have known?
The false positive in this case resulted from mosaicism, where the cells of the placenta showed abnormalities that the baby’s cells did not. According to a 1990 study:
Most instances of mosaicism detected in CVS are not associated with a fetal abnormality and should be evaluated by further prenatal testing, i.e., amniocentesis or fetal blood sampling. Because of the frequency of chromosomal mosaicism in CVS and its attendant need for further testing, a discussion of mosaicism should be included in counseling prior to CVS.
The study’s authors stated that mosaicism occurs in 1 percent of CV samples, a proportion 10 times greater than what’s observed in newborns. Non-mosaic false positives accounted for an additional 0.11 percent of CV samples. But here’s what’s being missed: a false positive rate of 0.15 percent (or multiple times that, based on the study) doesn’t mean there’s a 0.15 percent chance a positive result is false—it means that 0.15 percent of CV samples of normal babies will yield a false positive.
To really examine the accuracy of prenatal testing, you have to look at the positive predictive value (PPV)—the percentage of all positive tests that reflect true positives, or, put another way, the probability that a positive test result reflects an actual abnormality in the child. For chorionic villus sampling, the PPV is 72.6-78.3 percent, according to a 1992 study in Denmark.
A prenatal test’s PPV can be higher or lower depending on other factors, such as maternal age. But it is not unlikely that for some women, the odds of a positive CVS test being wrong could be one in four.
False Positives Aren’t Discussed Well, or Often Enough
False positive rates are mentioned much more often in popular prenatal literature than the PPV, though, and can give unfounded confidence to couples who agree to these tests. That confidence, reinforced by medical professionals, sometimes leads them to choose abortion. In a co-signed letter to the editor in the American Journal of Obstetrics and Gynecology, three medical doctors affirmed that “PPVs are more valuable to clinicians than detection rates.”
They advised caution when using CVS as a diagnostic to confirm less accurate prenatal screening results because CVS’s accuracy was established on tests of older women at greater risk for non-mosaic abnormalities. “An abnormal CVS result should not be considered fully diagnostic,” they wrote. Positive results from early Non-Invasive Prenatal Screening (NIPS or NIPT) confirmed by CVS “need confirmation through amniocentesis or ultrasound scans to prevent termination of a normal pregnancy.”
Other prenatal tests produce far more false positives than CVS but are nonetheless advertised to pregnant women and their partners as highly accurate. A study published in 2014 analyzed the blood samples from 1914 women from 21 different centers in the United States who were subjected to both standard and cell-free DNA testing—the scientifically specific term for what is in shorthand referred to as NIPT. Its authors found positive predictive values of 45.5 percent for Trisomy 21 and 40 percent for Trisomy 18 with cell-free DNA testing (see Table 3).
That means that according to this “accurate” early testing, 54.5 percent of women who were told their child likely had Down Syndrome delivered (or would have delivered) non-DS babies, and 60 percent who were told their child probably has Edward Syndrome delivered (or would have delivered) non-ES babies. Notably, 17 patients who received positive results with the standard screening in the aforementioned 2014 study of cell-free DNA testing went on for invasive testing (five with CVS and 22 with amniocentesis), which ruled out fetal abnormalities in all cases.
Researchers from Baylor and Hong Kong studied positive results from several different brands of NIPT and found that about 22 percent of all positives studied were false (69 out of 307). For the popular Harmony test, researchers from UCSF, Columbia University, and Ariosa (which created the Harmony test) found:
The positive predictive value of the Harmony test was 80.9 percent, comparing favorably to just 3.4 percent for standard screening. For women under the age of 35 only, the positive predictive value of NIPT decreased to 76 percent, and for women considered low-risk based on standard screening, it was 50 percent, still outperforming current first trimester screening. (Emphasis mine.)
While every patient’s scenario is unique and other clinical factors have to be taken into consideration, knowing the average PPV for a category into which many women fall (at least three-quarters of birthing women would have a PPV of three in four, according to census data) seems like an important piece of patient education.
The “standard tests” of quad screens or nuchal translucency tests, outperformed by NIPT, are indeed highly inaccurate. One analysis put their combined PPV at one in 18 with a false positive rate of 6.9 percent for Trisomy 21, while another more recent study published in the Journal of Prenatal Medicine found the popular “combination test” of nuchal translucency and serum screening has a PPV of 9.0 percent for Trisomy 21 and a false positive rate of 5 percent.
So by comparison, yes, cell-free DNA tests are more accurate. The companies that offer NIPTs seem to be quite comfortable letting pregnant mothers put their confidence in statements like “most proven” and “more accurate than standard testing.” It’s good for business. As the above letter to the editor put it, “When the detection rate is close to 100% (as in the case for trisomy 21), it may provide a misleading view on noninvasive prenatal testing (NIPT) and suggest that it is actually a diagnostic test.”
It’s much more comforting to read that the false positive rate is only 0.1 percent (touted on the Harmony Test FAQ page) than to read there’s a one in five chance (or, for mothers under 35, a one in four chance) that your baby is totally fine despite a positive result.
NIPT Companies Want to Promote Confidence
Knowing the PPV could be excruciating for women who consider abortion a valid option in case of fetal abnormality. Imagine being a pregnant mother younger than 35, getting a positive result, and thinking to yourself, “But what if he’s totally fine? What if he’s the one in four?”
Instead, the emphasis is put on the efficacy of the test in catching 99 percent of Down Syndrome cases and similarly high percentages of Trisomies 18 and 13. NIPT manufacturers promote the idea that identifying major abnormalities should be almost the sole concern for parents undergoing screening; whether a mother might abort a perfectly healthy baby in the effort to prevent an abnormal birth is nearly inconsequential.
As far as secondary diagnostics to confirm or reject screening results, Harmony, at least, utilizes misleading language. A slide in their “Expecting Parents” section reads:
Non-invasive prenatal testing (NIPT) uses cell-free DNA (cfDNA) derived from the pregnancy to evaluate possible chromosomal conditions in a pregnancy. NIPT is a prenatal screening test that can be performed as early as 10 weeks of pregnancy using a single blood draw. Prenatal diagnostic tests such as amniocentesis and CVS diagnose the presence of chromosomal conditions. They are typically performed later in pregnancy and are associated with a small risk of pregnancy loss.
Their FAQ section contains the following statement:
The Harmony prenatal test is also much less likely than traditional tests to give you a false-positive result, meaning there is much less chance your doctor would recommend follow-up invasive testing like amniocentesis.
The Harmony prenatal test is a screening test. Results should be confirmed with diagnostic testing such as amniocentesis and chorionic villus sampling (CVS).
Now, they could mean that since you are less likely to receive a positive result in the first place, you’re at a lower risk for more risky follow-up testing. But expecting couples could easily read that first sentence as an assurance a positive result really means their baby has an abnormality and that it may be enough to make a decision about “continuing the pregnancy.”
Even this 2016 clinician-facing document from Harmony (found at a URL in tiny print in the bottom corner of the last page of a sample test report) about the PPV states that the newfound attention paid to the PPV “challenges providers and laboratories alike since there is no precedent for either clinical discussion or reporting of PPV in previous methods of aneuploidy screening, i.e., serum analyte screening. The purpose of this paper is to address these issues” (emphasis mine).
If they really do value PPV as part of patient education, however, one would think they’d include a discussion of its benefits and limitations on their FAQ page. I reached out to Roche, the company that now owns Harmony, for comment, but they did not respond by time of publication.
Misleading Results Artificially Increase Abortions
Misleading statements are nothing new in the marketing of medical products and services. But does the trust of patients and doctors in inaccurate testing lead to more than a handful of abortions? There is evidence to suggest so.
In a small retrospective study of women with positive cell-free DNA test results conducted by researchers from Harvard, Brigham and Women’s Hospital, and Diagnostic Ultrasound Associates between 2012 and 2014, the termination rate was 66 percent (56/84). One-fifth of those abortions (19.6 percent or 11 fetuses) were done “for suspected autosomal trisomy without karyotype confirmation,” making up 13.1 percent of positive results for autosomal (non-sex chromosome) trisomy. That is to say, 13.1 percent of women who received positive results for trisomy aborted based on screening alone.
Given the authors’ stated PPV for cell-free DNA testing (used alone) of 58.6 percent, statistically, four to five of those unconfirmed terminations followed from false positives, constituting 4.8-6.0 percent of the total. Based on the sparse data available, the termination rates after secondary diagnostic tests of CVS (PPV ~75 percent) or amniocentesis (PPV 92 percent) could range from 53 percent (45/84) to perhaps as high as 82.9 percent. It would follow statistically that a significant number of non-trisomy babies are aborted even after diagnostic tests.
All Human Life Should Be Carried to Term
None of this is meant to imply that only healthy babies should be carried to term—that’s a reprehensible position. All human life has value; all humans are image bearers of God. The abysmal proportion of positive prenatal tests that are false is only as consequential as it is because abortion is legal in most of the places where it is used. Not only has the widespread use of prenatal testing practically wiped out the Down Syndrome population in Iceland and Denmark, but it is also prompting mothers and fathers across the world to unwittingly abort normal babies.
If abortion were illegal, couples with positive screening results would not be pressured into abortions by their health-care providers. It would no longer be “an agonizing decision.” It would be, with proper disincentives built into the legal system, a non-starter.
Instead, we have built ableist societies in which people with disabilities or life-limiting conditions are devalued to the point where we accept and even encourage their destruction in the womb, and where mothers and fathers who refuse to participate in death culture struggle to find support during (and after) the pregnancy.
The inaccuracy of prenatal testing isn’t just another misunderstood medical issue. When we try to play God, we pass judgment on those who reject our moral authority and sentence them to despair, pariah status, and a lifelong uphill battle just to have people recognize the dignity of their disabled or life-limited loved ones. When we try to play God, we get more death than we bargained for.
It’s one thing for medical professionals to passively play off of misconceptions about the accuracy of prenatal testing. It’s wholly another for it to do so when the consequences are literal life and death.
Correction: This sentence earlier stated “one in four” instead of “three in four”: “at least three-quarters of birthing women would have a PPV of three in four, according to census data…”