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Are We Doing the Wrong Prenatal Tests?

Updated: Dec 6, 2022

If a vendor pitches you a series of tests for employees where most of the positive results are false, leading to great stress and expense but no actionable results, you would presumably pass.

Whereas if a vendor pitches you a single simple blood test that can save your employees considerable stress and expense, you would say: “Where do I sign?”

Unfortunately, in the case of prenatal testing, the vast majority of carriers and employers are doing the opposite. They are inadvertently covering exactly the tests whose positive results are wrong most of the time, while not covering the biomarker that predicts pregnancy's #1 bad outcome – prematurity – in plenty of time to mitigate it.

This mixup is, as mentioned, inadvertent. The inaccurate tests are supported by large salesforces and direct-to-pregnant consumer and direct-to-obstetrician marketing campaigns. As a result, many insurers have been pressured into covering them, and unless a self-insured employer opts out, the tests get covered. [While this column dates from early 2022, these tests were also the subject of a recent expose.]

Whereas the very useful test, PreTRM, is still new to the market.

They say it takes 17 years for a medical advance to fully penetrate, but understanding false positive arithmetic will clarify why it makes a great deal of sense to cover PreTRM now instea. At the same time, understanding false positive arithmetic will reveal a more realistic view of the accuracy of the much more popular prenatal tests.


False Positive Arithmetic

Let’s step back to look at false positive arithmetic for screening in general. “Screening” differs from testing. The latter is performed specifically on patients who report to a doctor with symptoms. The former is done generally on a population meeting certain specs (like age or gender), to identify a previously undetected or otherwise undetectable problem in employees/patients with no current symptoms.

Consider heart attacks. Surely, if an employer could screen employees to predict and prevent a heart attack with 90% accuracy, that would be cost-effective. Or would it be?

The math says otherwise. Maybe two in every thousand employees will have a heart attack in any given year. Of those, at least one, if not more, fit one of the following descriptions:

  1. already have a known CAD diagnosis, diabetes, or metabolic syndrome (and hence screening won’t yield any new insights), or

  2. are among the many people whose heart attacks are completely unpredictable from a standard blood test.

Optimistically, then, you’re looking at a 1-in-1000 chance of actually finding an undiagnosed employee who would have a heart attack unless it is predicted and somehow prevented.

Let’s further assume that — highly optimistically and despite not being legally able to inquire about the huge risk factor of family history — the cardiac tests that a wellness vendor runs on an employee can predict a heart attack with 90% accuracy. Anyone who could predict heart attacks with 90% accuracy would win a Nobel Prize, so this is a very generous assumption.

Watch what happens when that 90%-accurate test is performed on a population of 1000 employees. First, the good news: there is indeed a 90% chance that the 1-in-1000 employee who would infarct can be found. That’s the single true positive. Next, the bad news. A 90%-accurate test is also 10% inaccurate, which means 10% of the other 999 employees will have a false positive.

As you can see, about 100 employees in total will test positive. 99 of those positive results will be false. And yet all 100 will be sent to the doctor, and likely subjected to a barrage of further tests and possible stents. Lab test arithmetic explains why it costs about $1-million for an employer to prevent a heart attack, assuming it can be prevented at all.

Here is another example of false positives, from breast cancer screening. The numbers are not precise but are used to illustrate the point:

The difference is that breast cancer is both common enough and treatable enough the US Preventive Services Task Force does endorse screening. Hence the false positives are, in their view, tolerable.


How does false positive arithmetic misdirect prenatal testing?

The tests that are considered in the remainder of this posting are called Non-Invasive Prenatal Tests, or NIPTs for short.

Along with Down Syndrome, a standard and widely covered test with a high accuracy rate, vendors are now selling a set of five or more NIPTs to predict disorders so rare that even trivia buffs like us here at Quizzify would whiff on Final Jeopardy.

Those marketing campaigns are remarkably successful, as it’s estimated that 30% of pregnant women get some or all these tests.

The irony is that learning about any chromosomal disorders in advance is not helpful, since they can’t be remediated in utero. That’s why the tests are generally marketed, as below, to provide “peace of mind” to the vast majority of women (those who test negative) rather than as a remediable issue for those who test positive.

Here are the accuracy rates of positive tests for all of these very rare abnormalities, as a summary. I would also encourage you to read the full exposé on these tests, and also the Letters to the Editor about them.

What happens if you get a positive (bad) result? You need to follow up with much more invasive, expensive amniocentesis. Not to mention the stress that goes along with a positive result. Even though, as you can see above, your chance of a positive result correctly indicating the abnormality in question are 20% or less.

Our recommendation to employers is to “precertify” employees by incentivizing them to take Quizzify’s pregnancy quiz, which educates on this false positive issue. Our Q&A format, with Learn More links, allows employees to figure out for themselves whether they want to order these NIPTs. They may decide to pass on NIPTs altogether. If they don't, they won't stress remotely as much if they get a positive result.


The Single Most Important Prenatal Test

Despite the popularity of – and insurance coverage for – these esoteric NIPTs, the most useful prenatal test, PreTRM to predict the risk of premature delivery, is severely underutilized.

PreTRM differs from NIPTs in three major ways. Indeed, the only similarity is that they are screens done during pregnancy. Otherwise, they couldn't be more different.

First, premature delivery is not a 1-in-10,000 event like the chromosomal abnormalities in the table above. It isn’t even 1-in-100. It’s closest to 1-in-10.

Second, PreTRM is predicting a risk which is, in fact, remediable. There are many tried-and-true interventions for high-risk mothers.

Third and speaking of which, unlike chromosomal abnormalities where either a baby has it or the test is wrong, there are degrees of preterm birth. The higher the risk score, the more likely a baby is to be born earlier, providing physicians with additional information with which to make more appropriate treatment decisions.

Since the most effective of these programs are also the most inconvenient and uncomfortable, obstetricians tend to limit them to women who are truly the highest risk. A test that identifies degrees of risk helps match the risk level to the intervention.

Now, let’s go back to the table above and contrast PreTRM to the NIPTs:

As you can see, the PreTRM test is up to 10 times more accurate for a concern that is 400 to 4000 times more prevalent, in addition to being infinitely more remediable.


To summarize, your best bet to exercise your ERISA fiduciary responsibility as a plan sponsor would be to cover PreTRM. And not just to fully cover the cost of a subsequent high-risk maternity program, but also (in the case of hourly employees) to pay for the hours needed to comply. You want to encourage participation in such a program, as every extra day in the womb doesn't just avoid or reduce NICU stays and expense, but also lowers the likelihood of a very long list of developmental complications.

If you do cover the NIPTs (and there are good arguments for covering them too, as long as the arithmetic is understood), incentivize employees to take Quizzify pregnancy quiz first, so that they understand this “false positive” arithmetic. Besides nudging some employees to pass on NIPTs altogether, a little knowledge would reduce the level of stress and expense for any who test positive.

Whether or not you cover any or all of these tests, the Quizzify pregnancy quiz is very useful for all your employees who are pregnant or considering it. Further, Quizzify2Go offers two full set of questions to discuss with your obstetrician during your a question set specifically about NIPTs.


Disclosure: Sera is a recipient of a Quizzify Valid Vendor award. The rules are described here. Most importantly, in joint accounts, Quizzify puts one-third of our own fees at risk for the performance of a Valid Vendor. This is in addition to our own 100% fee guarantee.


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